RE: Turn on compiler warnings by default for AC_PROG_CC, AC_PROG_CXX & AC_PROG_FC

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 6795fcb..2c13296 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -7160,7 +7160,7 @@ makes this invalid.  That is why Autoconf stopped issuing
 @end table
 
 @anchor{AC_PROG_CC}
-@defmac AC_PROG_CC (@ovar{compiler-search-list})
+@defmac AC_PROG_CC (@ovar{compiler-search-list}, @dots{})
 @acindex{PROG_CC}
 @evindex CC
 @evindex CFLAGS
@@ -7213,6 +7213,17 @@ other compilers.  If your package does not like this default, then it is
 acceptable to insert the line @samp{: $@{CFLAGS=""@}} after @code{AC_INIT}
 and before @code{AC_PROG_CC} to select an empty default instead.
 
+Scan for common flags that enable compiler warnings. If found, append them
+to @code{CFLAGS}. To modify this behaviour, for example, to restore the old
+no-warning-flag behaviour, add parameters which will get shifted by 1, 
+and passed on to @code{AC_FLAGS_WARN_ALL}. The following example adds a no-op
+fourth parameter, which becomes the third parameter to 
+@code{AC_FLAGS_WARN_ALL}, suppressing the default addition of warning flags.
+
+@example
+AC_PROG_CC([], [], [], [:])
+@end example
+
 Many Autoconf macros use a compiler, and thus call
 @samp{AC_REQUIRE([AC_PROG_CC])} to ensure that the compiler has been
 determined before the body of the outermost @code{AC_DEFUN} macro.
@@ -7537,7 +7548,7 @@ compiler fix the header files automatically when installed.
 @subsection C++ Compiler Characteristics
 
 
-@defmac AC_PROG_CXX (@ovar{compiler-search-list})
+@defmac AC_PROG_CXX (@ovar{compiler-search-list}, @dots{})
 @acindex{PROG_CXX}
 @evindex CXX
 @evindex CXXFLAGS
@@ -7599,6 +7610,18 @@ systems where G++ does not accept @option{-g}), or @option{-g} for other
 compilers.  If your package does not like this default, then it is
 acceptable to insert the line @samp{: $@{CXXFLAGS=""@}} after @code{AC_INIT}
 and before @code{AC_PROG_CXX} to select an empty default instead.
+
+Scan for common flags that enable compiler warnings. If found, append them
+to @code{CXXFLAGS}. To modify this behaviour, for example, to restore the old
+no-warning-flag behaviour, add parameters which will get shifted by 1, 
+and passed on to @code{AC_FLAGS_WARN_ALL}. The following example adds a no-op
+fourth parameter, which becomes the third parameter to 
+@code{AC_FLAGS_WARN_ALL}, suppressing the default addition of warning flags.
+
+@example
+AC_PROG_CXX([], [], [], [:])
+@end example
+
 @end defmac
 
 @defmac AC_PROG_CXXCPP
@@ -7825,7 +7848,7 @@ The result of the GNU test is cached in the
 @code{ac_cv_prog_f77_g} variable.
 @end defmac
 
-@defmac AC_PROG_FC (@ovar{compiler-search-list}, @ovar{dialect})
+@defmac AC_PROG_FC (@ovar{compiler-search-list}, @ovar{dialect}, @dots{})
 @acindex{PROG_FC}
 @evindex FC
 @evindex FCFLAGS
@@ -7863,6 +7886,19 @@ set @code{FCFLAGS} to @option{-g} for all other Fortran compilers.
 The result of the GNU test is cached in the @code{ac_cv_fc_compiler_gnu}
 variable, acceptance of @option{-g} in the @code{ac_cv_prog_fc_g}
 variable.
+
+Scan for common flags that enable compiler warnings. If found, append them
+to @code{FCFLAGS}. To modify this behaviour, for example, to restore the old
+no-warning-flag behaviour, add parameters which will get shifted by 2, 
+and passed on to @code{AC_FLAGS_WARN_ALL}. The following example adds a no-op
+fifth parameter, which becomes the third parameter to 
+@code{AC_FLAGS_WARN_ALL}, suppressing the default addition of warning flags.
+
+@example
+AC_PROG_FC([], [], [], [], [:])
+@end example
+
+
 @end defmac
 
 @defmac AC_PROG_F77_C_O
@@ -23444,6 +23480,127 @@ The current language does not change.  @code{AC_LANG_PUSH} is preferred
 (@pxref{AC_LANG_PUSH}).
 @end defmac
 
+@anchor{AC_CFLAGS_WARN_ALL}
+@defmac AC_CFLAGS_WARN_ALL(@var{shell-variable-to-add-to}, @var{add-value-if-not-found}, @var{action-if-found}, @var{action-if-not-found})
+@acindex{CFLAGS_WARN_ALL}
+Try to find a C compiler option that enables most reasonable warnings. See
+@pxref{AC_FLAGS_WARN_ALL} for how to use the (optional) parameters. The most
+typical usage is shown below. 
+
+@example
+AC_CFLAGS_WARN_ALL
+@end example
+@end defmac
+
+@anchor{AC_CXXFLAGS_WARN_ALL}
+@defmac AC_CXXFLAGS_WARN_ALL(@var{shell-variable-to-add-to}, @var{add-value-if-not-found}, @var{action-if-found}, @var{action-if-not-found})
+@acindex{CXXFLAGS_WARN_ALL}
+Try to find a C++ compiler option that enables most reasonable warnings. See
+@pxref{AC_FLAGS_WARN_ALL} for how to use the (optional) parameters. The most
+typical usage is shown below. 
+
+@example
+AC_CXXFLAGS_WARN_ALL
+@end example
+@end defmac
+
+@anchor{AC_FCFLAGS_WARN_ALL}
+@defmac AC_FCFLAGS_WARN_ALL(@var{shell-variable-to-add-to}, @var{add-value-if-not-found}, @var{action-if-found}, @var{action-if-not-found})
+@acindex{FCFLAGS_WARN_ALL}
+Try to find a Fortran compiler option that enables most reasonable warnings.
+See @pxref{AC_FLAGS_WARN_ALL} for how to use the (optional) parameters. The most
+typical usage is shown below. 
+
+@example
+AC_FCFLAGS_WARN_ALL
+@end example
+@end defmac
+
+@anchor{AC_FLAGS_WARN_ALL}
+@defmac AC_FLAGS_WARN_ALL(@var{shell-variable-to-add-to}, @var{add-value-if-not-found}, @var{action-if-found}, @var{action-if-not-found})
+@acindex{FLAGS_WARN_ALL}
+Try to find a compiler option that enables most reasonable warnings. 
+
+Usually not used directly. Instead, use @pxref{AC_CFLAGS_WARN_ALL}, 
+@pxref{AC_CXXFLAGS_WARN_ALL}, or @pxref{AC_FCFLAGS_WARN_ALL}, all of which perform
+a requisite @pxref{AC_LANG_PUSH}, and then invoke this macro without altering any
+positional parameters they were provided. 
+
+The first positional parameter defines the shell variable to use, and
+if not provided, depends on @pxref{AC_LANG_PUSH} having been invoked properly.
+If appropriate warning flag values can be automatically determined for the
+compiler, then the third positional parameter (if present) defines an
+alternate action to take instead of appending to the shell variable. If no
+appropriate warning flag values could be determined, then the second
+positional parameter (if present) defines alternate flags to append to the
+shell variable, unless the fourth positional parameter is present, in which
+case it defines an alternate action to take instead of appending to the shell
+variable.
+@end defmac
+
+@anchor{AC_APPEND_FLAG}
+@defmac AC_APPEND_FLAG(@var{add-value})
+@acindex{APPEND_FLAG}
+Used internally by @pxref{AC_FLAGS_WARN_ALL}. Behavior is to append the given to
+the shell variable determined or provided in the call to
+@pxref{AC_FLAGS_WARN_ALL}, but only if it is not already present there.
+@end defmac
+
+@anchor{AC_APPEND_CFLAG_IFVALID}
+@defmac AC_APPEND_CFLAG_IFVALID(@var{add-value})
+@acindex{APPEND_CFLAG_IFVALID}
+Sets the current language to C, then invokes @pxref{AC_APPEND_FLAG_IFVALID}.
+The following example shows a typical usage, adding @option{-Wfancy-warnings} 
+on top of whatever warning flags are already added for the current C
+compiler, but only if @option{-Wfancy-warnings} is a valid flag.
+
+@example
+AC_PROG_CC
+AC_APPEND_CFLAG_IFVALID([-Wfancy-warnings])
+@end example
+
+@end defmac
+
+@anchor{AC_APPEND_CXXFLAG_IFVALID}
+@defmac AC_APPEND_CXXFLAG_IFVALID(@var{add-value})
+@acindex{APPEND_CXXFLAG_IFVALID}
+Sets the current language to C++, then invokes @pxref{AC_APPEND_FLAG_IFVALID}.
+The following example shows a typical usage, adding @option{-Wfancy-warnings} 
+on top of whatever warning flags are already added for the current C++
+compiler, but only if @option{-Wfancy-warnings} is a valid flag.
+
+@example
+AC_PROG_CXX
+AC_APPEND_CXXFLAG_IFVALID([-Wfancy-warnings])
+@end example
+
+@end defmac
+
+@anchor{AC_APPEND_FCFLAG_IFVALID}
+@defmac AC_APPEND_FCFLAG_IFVALID(@var{add-value})
+@acindex{APPEND_FCFLAG_IFVALID}
+Sets the current language to Fortran, then invokes 
+@pxref{AC_APPEND_FLAG_IFVALID}.
+The following example shows a typical usage, adding @option{-Wfancy-warnings} 
+on top of whatever warning flags are already added for the current Fortran
+compiler, but only if @option{-Wfancy-warnings} is a valid flag.
+
+@example
+AC_PROG_FC
+AC_APPEND_FCFLAG_IFVALID([-Wfancy-warnings])
+@end example
+@end defmac
+
+@anchor{AC_APPEND_FLAG_IFVALID}
+@defmac AC_APPEND_FLAG_IFVALID(@var{add-value})
+@acindex{APPEND_FLAG_IFVALID}
+Used internally by @pxref{AC_APPEND_CFLAG_IFVALID}, 
+@pxref{AC_APPEND_CXXFLAG_IFVALID}, and @pxref{AC_APPEND_FCFLAG_IFVALID}. 
+Determine the appropriate compiler flags variable for the current language, 
+compile a test program using the given flag(s), and if the compile process
+exits normally, append it to the flags variable using @pxref{AC_APPEND_FLAG}.
+@end defmac
+
 @defmac AC_LINK_FILES (@var{source}@dots{}, @var{dest}@dots{})
 @acindex{LINK_FILES}
 This is an obsolete version of @code{AC_CONFIG_LINKS}
diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
index f0f6667..0731202 100644
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -424,11 +424,17 @@ AU_DEFUN([ac_cv_prog_gcc],
 [ac_cv_c_compiler_gnu])
 
 
-# AC_PROG_CC([COMPILER ...])
+# AC_PROG_CC([COMPILER ...], ...)
 # --------------------------
 # COMPILER ... is a space separated list of C compilers to search for.
 # This just gives the user an opportunity to specify an alternative
 # search list for the C compiler.
+# Any extra parameters will be passed on to AC_FLAGS_WARN_ALL. If there
+# are no extra parameters, then compiler warnings will be turned on. An
+# example of how to avoid this is invoking
+# AC_PROG_CC([COMPILER ...], [], [], [echo No extra warnings please.])
+# Where the final parameter is providing an alternate action to enabling
+# warning flags.
 AN_MAKEVAR([CC],  [AC_PROG_CC])
 AN_PROGRAM([cc],  [AC_PROG_CC])
 AN_PROGRAM([gcc], [AC_PROG_CC])
@@ -491,6 +497,7 @@ _AC_PROG_CC_C11([ac_prog_cc_stdc=c11
 		      [ac_prog_cc_stdc=no
 		       ac_cv_prog_cc_stdc=no])])])
 dnl
+AC_FLAGS_WARN_ALL(m4_shift($@))
 AC_LANG_POP(C)dnl
 ])# AC_PROG_CC
 
@@ -674,7 +681,7 @@ AU_DEFUN([ac_cv_prog_gxx],
 [ac_cv_cxx_compiler_gnu])
 
 
-# AC_PROG_CXX([LIST-OF-COMPILERS])
+# AC_PROG_CXX([LIST-OF-COMPILERS], ...)
 # --------------------------------
 # LIST-OF-COMPILERS is a space separated list of C++ compilers to search
 # for (if not specified, a default list is used).  This just gives the
@@ -686,6 +693,12 @@ AU_DEFUN([ac_cv_prog_gxx],
 # RCC	Rational C++
 # xlC_r	AIX C Set++ (with support for reentrant code)
 # xlC	AIX C Set++
+# Any extra parameters will be passed on to AC_FLAGS_WARN_ALL. If there
+# are no extra parameters, then compiler warnings will be turned on. An
+# example of how to avoid this is invoking
+# AC_PROG_CXX([LIST-OF-COMPILERS], [], [], [echo No extra warnings please.])
+# Where the final parameter is providing an alternate action to enabling
+# warning flags.
 AN_MAKEVAR([CXX],  [AC_PROG_CXX])
 AN_PROGRAM([CC],   [AC_PROG_CXX])
 AN_PROGRAM([c++],  [AC_PROG_CXX])
@@ -732,6 +745,7 @@ _AC_PROG_CXX_CXX11([ac_prog_cxx_stdcxx=cxx11
 		        ac_cv_prog_cxx_stdcxx=$ac_cv_prog_cxx_cxx98],
 		       [ac_prog_cxx_stdcxx=no
 		        ac_cv_prog_cxx_stdcxx=no])])
+AC_FLAGS_WARN_ALL(m4_shift($@))
 AC_LANG_POP(C++)dnl
 ])# AC_PROG_CXX
 
diff --git a/lib/autoconf/fortran.m4 b/lib/autoconf/fortran.m4
index e0f66f1..e013d28 100644
--- a/lib/autoconf/fortran.m4
+++ b/lib/autoconf/fortran.m4
@@ -371,10 +371,16 @@ AC_LANG_POP(Fortran 77)dnl
 ])# AC_PROG_F77
 
 
-# AC_PROG_FC([COMPILERS...], [DIALECT])
+# AC_PROG_FC([COMPILERS...], [DIALECT], ...)
 # -------------------------------------
 # COMPILERS is a space separated list of Fortran 77 compilers to search
 # for, and [DIALECT] is an optional dialect.  See also _AC_PROG_FC.
+# Any extra parameters will be passed on to AC_FLAGS_WARN_ALL. If there
+# are no extra parameters, then compiler warnings will be turned on. An
+# example of how to avoid this is invoking
+# AC_PROG_FC([COMPILERS...], [DIALECT], [], [], [echo No extra warnings please.])
+# Where the final parameter is providing an alternate action to enabling
+# warning flags.
 AC_DEFUN([AC_PROG_FC],
 [AC_LANG_PUSH(Fortran)dnl
 AC_ARG_VAR([FC],    [Fortran compiler command])dnl
@@ -387,6 +393,7 @@ if test $ac_compiler_gnu = yes; then
 else
   GFC=
 fi
+AC_FLAGS_WARN_ALL(m4_shift2($@))
 AC_LANG_POP(Fortran)dnl
 ])# AC_PROG_FC
 
diff --git a/lib/autoconf/lang.m4 b/lib/autoconf/lang.m4
index b8cbe76..cbff0f4 100644
--- a/lib/autoconf/lang.m4
+++ b/lib/autoconf/lang.m4
@@ -719,3 +719,183 @@ ac_objext=$OBJEXT
 AC_DEFUN([AC_LANG_WERROR],
 [m4_divert_text([DEFAULTS], [ac_[]_AC_LANG_ABBREV[]_werror_flag=])
 ac_[]_AC_LANG_ABBREV[]_werror_flag=yes])# AC_LANG_WERROR
+
+#
+# SYNOPSIS
+#
+#   AC_APPEND_FLAG(FLAG, [FLAGS-VARIABLE])
+#
+# DESCRIPTION
+#
+#   FLAG is appended to the FLAGS-VARIABLE shell variable, with a space
+#   added in between.
+#
+#   If FLAGS-VARIABLE is not specified, the current language's flags (e.g.
+#   CFLAGS) is used.  FLAGS-VARIABLE is not changed if it already contains
+#   FLAG.  If FLAGS-VARIABLE is unset in the shell, it is set to exactly
+#   FLAG.
+#
+#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION.
+#   NOTE: Copied from AX_APPEND_FLAG in autoconf-archive, which had copyright
+#         assigned as follows:
+#
+#           Copyright (c) 2008 Guido U. Draheim <[email protected]>
+#           Copyright (c) 2011 Maarten Bosmans <[email protected]>
+#
+
+#serial 2
+
+AC_DEFUN([AC_APPEND_FLAG],
+[AS_VAR_PUSHDEF([FLAGS], [m4_default($2,_AC_LANG_PREFIX[FLAGS])])dnl
+AS_VAR_SET_IF(FLAGS,
+  [case " AS_VAR_GET(FLAGS) " in
+    *" $1 "*)
+      AC_RUN_LOG([: FLAGS already contains $1])
+      ;;
+    *)
+      AC_RUN_LOG([: FLAGS="$FLAGS $1"])
+      AS_VAR_SET(FLAGS, ["AS_VAR_GET(FLAGS) $1"])
+      ;;
+   esac],
+  [AS_VAR_SET(FLAGS,["$1"])])
+AS_VAR_POPDEF([FLAGS])dnl
+])dnl AC_APPEND_FLAG
+
+#
+# SYNOPSIS
+#
+#   AC_CFLAGS_WARN_ALL   [(shellvar [,default, [A/NA]])]
+#   AC_CXXFLAGS_WARN_ALL [(shellvar [,default, [A/NA]])]
+#   AC_FCFLAGS_WARN_ALL  [(shellvar [,default, [A/NA]])]
+#
+# DESCRIPTION
+#
+#   Try to find a compiler option that enables most reasonable warnings.
+#
+#   For the GNU compiler it will be -Wall (and -ansi -pedantic) The result
+#   is added to the shellvar being CFLAGS, CXXFLAGS, or FCFLAGS by default.
+#
+#   Currently this macro knows about the GCC, Solaris, Digital Unix, AIX,
+#   HP-UX, IRIX, NEC SX-5 (Super-UX 10), Cray J90 (Unicos 10.0.0.8), and
+#   Intel compilers.  For a given compiler, the Fortran flags are much more
+#   experimental than their C equivalents.
+#
+#    - $1 shell-variable-to-add-to : CFLAGS, CXXFLAGS, or FCFLAGS
+#    - $2 add-value-if-not-found : nothing
+#    - $3 action-if-found : add value to shellvariable
+#    - $4 action-if-not-found : nothing
+#
+#   NOTE: These macros depend on AX_APPEND_FLAG.
+#   NOTE: Based upon AX_*FLAGS_WARN_ALL from autoconf-archive, which had
+#         copyright assigned as follows:
+#
+#           Copyright (c) 2008 Guido U. Draheim <[email protected]>
+#           Copyright (c) 2010 Rhys Ulerich <[email protected]>
+#
+
+#serial 14
+
+AC_DEFUN([AC_FLAGS_WARN_ALL],[dnl
+AS_VAR_PUSHDEF([FLAGS],[_AC_LANG_PREFIX[]FLAGS])dnl
+AS_VAR_PUSHDEF([VAR],[ac_cv_[]_AC_LANG_ABBREV[]flags_warn_all])dnl
+AC_CACHE_CHECK([m4_ifval($1,$1,FLAGS) for maximum warnings],
+VAR,[VAR="no, unknown"
+ac_save_[]FLAGS="$[]FLAGS"
+for ac_arg dnl
+in "-warn all  % -warn all"   dnl Intel
+   "-pedantic  % -Wall"       dnl GCC
+   "-xstrconst % -v"          dnl Solaris C
+   "-std1      % -verbose -w0 -warnprotos" dnl Digital Unix
+   "-qlanglvl=ansi % -qsrcmsg -qinfo=all:noppt:noppc:noobs:nocnd" dnl AIX
+   "-ansi -ansiE % -fullwarn" dnl IRIX
+   "+ESlit     % +w1"         dnl HP-UX C
+   "-Xc        % -pvctl[,]fullmsg" dnl NEC SX-5 (Super-UX 10)
+   "-h conform % -h msglevel 2" dnl Cray C (Unicos)
+   #
+do FLAGS="$ac_save_[]FLAGS "`echo $ac_arg | sed -e 's,%%.*,,' -e 's,%,,'`
+   _AC_COMPILE_IFELSE([AC_LANG_PROGRAM],
+                     [VAR=`echo $ac_arg | sed -e 's,.*% *,,'` ; break])
+done
+FLAGS="$ac_save_[]FLAGS"
+VAR=m4_ifvaln($3,[ignored],[$VAR])
+])
+AS_VAR_POPDEF([FLAGS])dnl
+AC_REQUIRE([AC_APPEND_FLAG])
+case ".$VAR" in
+     .ok|.ok,*) m4_ifvaln($3,$3) ;;
+   .|.no|.no,*) m4_default($4,[m4_ifval($2,[AC_APPEND_FLAG([$2], [$1])])]) ;;
+   *) m4_default($3,[AC_APPEND_FLAG([$VAR], [$1])]) ;;
+esac
+AS_VAR_POPDEF([VAR])dnl
+])dnl AC_FLAGS_WARN_ALL
+dnl  implementation tactics:
+dnl   the for-argument contains a list of options. The first part of
+dnl   these does only exist to detect the compiler - usually it is
+dnl   a global option to enable -ansi or -extrawarnings. All other
+dnl   compilers will fail about it. That was needed since a lot of
+dnl   compilers will give false positives for some option-syntax
+dnl   like -Woption or -Xoption as they think of it is a pass-through
+dnl   to later compile stages or something. The "%" is used as a
+dnl   delimiter. A non-option comment can be given after "%%" marks
+dnl   which will be shown but not added to the respective C/CXXFLAGS.
+
+#
+# SYNOPSIS
+#
+#   AC_APPEND_FLAG_IFVALID(FLAG)
+#
+# DESCRIPTION
+#
+# FLAG is tested as a compile flag. If the exit code is 0 for the text,
+# then it is appended to the flags.
+AC_DEFUN([AC_APPEND_FLAG_IFVALID],[dnl
+AS_VAR_PUSHDEF([FLAGS],[_AC_LANG_PREFIX[]FLAGS])dnl
+AC_MSG_CHECKING([validity of $1 in FLAGS])
+AFIV_TMP="no, unknown"
+ac_save_[]FLAGS="$[]FLAGS"
+FLAGS=$1
+_AC_COMPILE_IFELSE([AC_LANG_PROGRAM], [AFIV_TMP="$1"])
+FLAGS="$ac_save_[]FLAGS"
+AS_VAR_POPDEF([FLAGS])dnl
+AC_REQUIRE([AC_APPEND_FLAG])
+case ".$AFIV_TMP" in
+   .|.no|.no,*) AC_MSG_RESULT([no]) ;;
+   *) AC_APPEND_FLAG([$1]) AC_MSG_RESULT([yes]) ;;
+esac
+])dnl AC_APPEND_FLAG_IFVALID
+
+AC_DEFUN([AC_APPEND_CFLAG_IFVALID],[dnl
+AC_LANG_PUSH([C])
+AC_APPEND_FLAG_IFVALID([$1])
+AC_LANG_POP([C])
+])
+
+AC_DEFUN([AC_APPEND_CXXFLAG_IFVALID],[dnl
+AC_LANG_PUSH([C++])
+AC_APPEND_FLAG_IFVALID([$1])
+AC_LANG_POP([C++])
+])
+
+AC_DEFUN([AC_APPEND_FCFLAG_IFVALID],[dnl
+AC_LANG_PUSH([Fortran])
+AC_APPEND_FLAG_IFVALID([$1])
+AC_LANG_POP([Fortran])
+])
+
+AC_DEFUN([AC_CFLAGS_WARN_ALL],[dnl
+AC_LANG_PUSH([C])
+AC_FLAGS_WARN_ALL([$1], [$2], [$3], [$4])
+AC_LANG_POP([C])
+])
+
+AC_DEFUN([AC_CXXFLAGS_WARN_ALL],[dnl
+AC_LANG_PUSH([C++])
+AC_FLAGS_WARN_ALL([$1], [$2], [$3], [$4])
+AC_LANG_POP([C++])
+])
+
+AC_DEFUN([AC_FCFLAGS_WARN_ALL],[dnl
+AC_LANG_PUSH([Fortran])
+AC_FLAGS_WARN_ALL([$1], [$2], [$3], [$4])
+AC_LANG_POP([Fortran])
+])