[PATCH] configure.ac: fix AC_CHECK_HEADER call to test for libssh2

Building nmap as a part of the buildroot fails because in the
configure.ac test for libssh2 -lm is passed as an argument to
AC_CHECK_HEADER() instead of the AC_CHECK_LIB().

---

The patch below fixes this configure.ac bit and includes regenerated
configure script. Please consider applying this fix. For more details
please see the thread by the following URL:

  http://lists.busybox.net/pipermail/buildroot/2017-November/205936.html

---
Index: configure
===================================================================
--- configure	(revision 37072)
+++ configure	(working copy)
@@ -5552,8 +5552,8 @@
 
         if test -n "$PYTHON"; then
       # If the user set $PYTHON, use it and don't search something else.
-      { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $PYTHON version >= 2.4" >&5
-$as_echo_n "checking whether $PYTHON version >= 2.4... " >&6; }
+      { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $PYTHON version is >= 2.4" >&5
+$as_echo_n "checking whether $PYTHON version is >= 2.4... " >&6; }
       prog="import sys
 # split strings by '.' and convert to numeric.  Append some zeros
 # because we need at least 4 digits for the hex conversion.
@@ -5571,7 +5571,9 @@
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 else
-  as_fn_error $? "too old" "$LINENO" 5
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+			       as_fn_error $? "Python interpreter is too old" "$LINENO" 5
 fi
       am_display_PYTHON=$PYTHON
     else
@@ -5690,6 +5692,25 @@
   PYTHON_PLATFORM=$am_cv_python_platform
 
 
+  # Just factor out some code duplication.
+  am_python_setup_sysconfig="\
+import sys
+# Prefer sysconfig over distutils.sysconfig, for better compatibility
+# with python 3.x.  See automake bug#10227.
+try:
+    import sysconfig
+except ImportError:
+    can_use_sysconfig = 0
+else:
+    can_use_sysconfig = 1
+# Can't use sysconfig in CPython 2.7, since it's broken in virtualenvs:
+# <https://github.com/pypa/virtualenv/issues/118>
+try:
+    from platform import python_implementation
+    if python_implementation() == 'CPython' and sys.version[:3] == '2.7':
+        can_use_sysconfig = 0
+except ImportError:
+    pass"
 
 
             { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $am_display_PYTHON script directory" >&5
@@ -5703,7 +5724,14 @@
      else
        am_py_prefix=$prefix
      fi
-     am_cv_python_pythondir=`$PYTHON -c "import sys; from distutils import sysconfig; sys.stdout.write(sysconfig.get_python_lib(0,0,prefix='$am_py_prefix'))" 2>/dev/null`
+     am_cv_python_pythondir=`$PYTHON -c "
+$am_python_setup_sysconfig
+if can_use_sysconfig:
+    sitedir = sysconfig.get_path('purelib', vars={'base':'$am_py_prefix'})
+else:
+    from distutils import sysconfig
+    sitedir = sysconfig.get_python_lib(0, 0, prefix='$am_py_prefix')
+sys.stdout.write(sitedir)"`
      case $am_cv_python_pythondir in
      $am_py_prefix*)
        am__strip_prefix=`echo "$am_py_prefix" | sed 's|.|.|g'`
@@ -5740,7 +5768,14 @@
      else
        am_py_exec_prefix=$exec_prefix
      fi
-     am_cv_python_pyexecdir=`$PYTHON -c "import sys; from distutils import sysconfig; sys.stdout.write(sysconfig.get_python_lib(1,0,prefix='$am_py_exec_prefix'))" 2>/dev/null`
+     am_cv_python_pyexecdir=`$PYTHON -c "
+$am_python_setup_sysconfig
+if can_use_sysconfig:
+    sitedir = sysconfig.get_path('platlib', vars={'platbase':'$am_py_prefix'})
+else:
+    from distutils import sysconfig
+    sitedir = sysconfig.get_python_lib(1, 0, prefix='$am_py_prefix')
+sys.stdout.write(sitedir)"`
      case $am_cv_python_pyexecdir in
      $am_py_exec_prefix*)
        am__strip_prefix=`echo "$am_py_exec_prefix" | sed 's|.|.|g'`
@@ -6801,8 +6836,7 @@
     CPPFLAGS="-I$with_libssh2/include $CPPFLAGS"
     LDFLAGS="-L$with_libssh2/lib $LDFLAGS"
 
-    ac_fn_c_check_header_compile "$LINENO" "libssh2.h" "ac_cv_header_libssh2_h" "-lm
-"
+    ac_fn_c_check_header_mongrel "$LINENO" "libssh2.h" "ac_cv_header_libssh2_h" "$ac_includes_default"
 if test "x$ac_cv_header_libssh2_h" = xyes; then :
 
       { $as_echo "$as_me:${as_lineno-$LINENO}: checking for libssh2_version in -lssh2" >&5
@@ -6811,7 +6845,7 @@
   $as_echo_n "(cached) " >&6
 else
   ac_check_lib_save_LIBS=$LIBS
-LIBS="-lssh2  $LIBS"
+LIBS="-lssh2 -lm $LIBS"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
Index: configure.ac
===================================================================
--- configure.ac	(revision 37072)
+++ configure.ac	(working copy)
@@ -674,7 +674,7 @@
       AC_CHECK_LIB(ssh2, libssh2_version,
         [have_libssh2=yes
         LIBSSH2_INC=$with_libssh2/include
-        LIBSSH2_LIB=$with_libssh2/lib])],,[-lm])
+        LIBSSH2_LIB=$with_libssh2/lib],,[-lm])])
 
     LDFLAGS=$_ldflags
     CPPFLAGS=$_cppflags
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