* extensions.m4 (gl_USE_SYSTEM_EXTENSIONS): Don't #define

[gnulib.git] / m4 / extensions.m4

diff --git a/m4/extensions.m4 b/m4/extensions.m4
index e71845f..5f22d42 100644 (file)
--- a/m4/extensions.m4
+++ b/m4/extensions.m4
@@ -1,6 +1,6 @@
 # Enable extensions on systems that normally disable them.
 
-# Copyright (C) 2003 Free Software Foundation, Inc.
+# Copyright (C) 2003, 2006 Free Software Foundation, Inc.
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
 # with or without modifications, as long as this notice is preserved.
@@ -25,6 +25,15 @@ AC_DEFUN([gl_USE_SYSTEM_EXTENSIONS], [
 #ifndef _POSIX_PTHREAD_SEMANTICS
 # undef _POSIX_PTHREAD_SEMANTICS
 #endif])
-  AC_DEFINE([__EXTENSIONS__])
+  AC_CACHE_CHECK([whether it is safe to define __EXTENSIONS__],
+    [ac_cv_safe_to_define___extensions__],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM([
+         #define __EXTENSIONS__ 1
+         AC_INCLUDES_DEFAULT])],
+       [ac_cv_safe_to_define___extensions__=yes],
+       [ac_cv_safe_to_define___extensions__=no])])
+  test $ac_cv_safe_to_define___extensions__ == yes &&
+    AC_DEFINE([__EXTENSIONS__])
   AC_DEFINE([_POSIX_PTHREAD_SEMANTICS])
 ])