[PATCH 1/2] ax_prog_cc_for_build: Fix BUILD_{EXE, OBJ}EXT for Autoconf 2.70

Autoconf 2.70 introduced a change in AC_SUBST behavior that the variable
name in AC_SUBST no longer gets macro expanded. This breaks the rename
syntaxes of BUILD_EXEEXT and BUILD_OBJEXT in AX_PROG_CC_FOR_BUILD.
Change to an alternative approach of assigning BUILD_EXEEXT and
BUILD_OBJEXT manually. The values of EXEEXT and OBJEXT have to be fixed
too at the end of the AX_PROG_CC_FOR_BUILD code.
---
 m4/ax_prog_cc_for_build.m4 | 39 +++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/m4/ax_prog_cc_for_build.m4 b/m4/ax_prog_cc_for_build.m4
index 1db8d73..0f92825 100644
--- a/m4/ax_prog_cc_for_build.m4
+++ b/m4/ax_prog_cc_for_build.m4
@@ -32,7 +32,7 @@
 # and this notice are preserved. This file is offered as-is, without any
 # warranty.

-#serial 21
+#serial 22

 AU_ALIAS([AC_PROG_CC_FOR_BUILD], [AX_PROG_CC_FOR_BUILD])
 AC_DEFUN([AX_PROG_CC_FOR_BUILD], [dnl
@@ -51,8 +51,6 @@ pushdef([ac_cv_prog_cc_works], ac_cv_build_prog_cc_works)dnl
 pushdef([ac_cv_prog_cc_cross], ac_cv_build_prog_cc_cross)dnl
 pushdef([ac_cv_prog_cc_g], ac_cv_build_prog_cc_g)dnl
 pushdef([ac_cv_c_compiler_gnu], ac_cv_build_c_compiler_gnu)dnl
-pushdef([ac_cv_exeext], ac_cv_build_exeext)dnl
-pushdef([ac_cv_objext], ac_cv_build_objext)dnl
 pushdef([ac_exeext], ac_build_exeext)dnl
 pushdef([ac_objext], ac_build_objext)dnl
 pushdef([CC], CC_FOR_BUILD)dnl
@@ -60,9 +58,7 @@ pushdef([CPP], CPP_FOR_BUILD)dnl
 pushdef([GCC], GCC_FOR_BUILD)dnl
 pushdef([CFLAGS], CFLAGS_FOR_BUILD)dnl
 pushdef([CPPFLAGS], CPPFLAGS_FOR_BUILD)dnl
-pushdef([EXEEXT], BUILD_EXEEXT)dnl
 pushdef([LDFLAGS], LDFLAGS_FOR_BUILD)dnl
-pushdef([OBJEXT], BUILD_OBJEXT)dnl
 pushdef([host], build)dnl
 pushdef([host_alias], build_alias)dnl
 pushdef([host_cpu], build_cpu)dnl
@@ -78,6 +74,21 @@ pushdef([am_cv_CC_dependencies_compiler_type],
am_cv_build_CC_dependencies_compi
 pushdef([am_cv_prog_cc_c_o], am_cv_build_prog_cc_c_o)dnl
 pushdef([cross_compiling], cross_compiling_build)dnl

+dnl These variables are problematic to rename by M4 macros, so we save
+dnl their values in alternative names, and restore the values later.
+dnl
+dnl _AC_COMPILER_EXEEXT and _AC_COMPILER_OBJEXT internally call
+dnl AC_SUBST which prevents the renaming of EXEEXT and OBJEXT
+dnl variables. It's not a good idea to rename ac_cv_exeext and
+dnl ac_cv_objext either as they're related.
+dnl Renaming ac_exeext and ac_objext is safe though.
+AS_VAR_SET_IF([ac_cv_exeext],
+ [ac_cv_host_exeext=$ac_cv_exeext
+ AS_UNSET([ac_cv_exeext])])
+AS_VAR_SET_IF([ac_cv_objext],
+ [ac_cv_host_objext=$ac_cv_objext
+ AS_UNSET([ac_cv_objext])])
+
 cross_compiling_build=no

 ac_build_tool_prefix=
@@ -120,9 +131,7 @@ popdef([host_vendor])dnl
 popdef([host_cpu])dnl
 popdef([host_alias])dnl
 popdef([host])dnl
-popdef([OBJEXT])dnl
 popdef([LDFLAGS])dnl
-popdef([EXEEXT])dnl
 popdef([CPPFLAGS])dnl
 popdef([CFLAGS])dnl
 popdef([GCC])dnl
@@ -130,8 +139,6 @@ popdef([CPP])dnl
 popdef([CC])dnl
 popdef([ac_objext])dnl
 popdef([ac_exeext])dnl
-popdef([ac_cv_objext])dnl
-popdef([ac_cv_exeext])dnl
 popdef([ac_cv_c_compiler_gnu])dnl
 popdef([ac_cv_prog_cc_g])dnl
 popdef([ac_cv_prog_cc_cross])dnl
@@ -140,6 +147,20 @@ popdef([ac_cv_prog_cc_c89])dnl
 popdef([ac_cv_prog_gcc])dnl
 popdef([ac_cv_prog_CPP])dnl

+BUILD_EXEEXT=$ac_cv_exeext
+BUILD_OBJEXT=$ac_cv_objext
+
+AS_VAR_SET_IF([ac_cv_host_exeext],
+ [ac_cv_exeext=$ac_cv_host_exeext
+ EXEEXT=$ac_cv_host_exeext],
+ [AS_UNSET([ac_cv_exeext])
+ AS_UNSET([EXEEXT])])
+AS_VAR_SET_IF([ac_cv_host_objext],
+ [ac_cv_objext=$ac_cv_host_objext
+ OBJEXT=$ac_cv_host_objext],
+ [AS_UNSET([ac_cv_objext])
+ AS_UNSET([OBJEXT])])
+
 dnl restore global variables ac_ext, ac_cpp, ac_compile,
 dnl ac_link, ac_compiler_gnu (dependant on the current
 dnl language after popping):
-- 
2.44.0