--- m4/extensions.m4
+++ m4/extensions.m4
@@ -1,14 +1,14 @@
-# serial 4  -*- Autoconf -*-
+# serial 5  -*- Autoconf -*-
 # Enable extensions on systems that normally disable them.
 
-# Copyright (C) 2003, 2006 Free Software Foundation, Inc.
+# Copyright (C) 2003, 2006-2008 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.
 
 # This definition of AC_USE_SYSTEM_EXTENSIONS is stolen from CVS
 # Autoconf.  Perhaps we can remove this once we can assume Autoconf
-# 2.61 or later everywhere, but since CVS Autoconf mutates rapidly
+# 2.62 or later everywhere, but since CVS Autoconf mutates rapidly
 # enough in this area it's likely we'll need to redefine
 # AC_USE_SYSTEM_EXTENSIONS for quite some time.
 
@@ -16,39 +16,63 @@
 # ------------------------
 # Enable extensions on systems that normally disable them,
 # typically due to standards-conformance issues.
+# Remember that #undef in AH_VERBATIM gets replaced with #define by
+# AC_DEFINE.  The goal here is to define all known feature-enabling
+# macros, then, if reports of conflicts are made, disable macros that
+# cause problems on some platforms (such as __EXTENSIONS__).
 AC_DEFUN([AC_USE_SYSTEM_EXTENSIONS],
-[
-  AC_BEFORE([$0], [AC_COMPILE_IFELSE])
-  AC_BEFORE([$0], [AC_RUN_IFELSE])
-
-  AC_REQUIRE([AC_GNU_SOURCE])
-  AC_REQUIRE([AC_AIX])
-  AC_REQUIRE([AC_MINIX])
+[AC_BEFORE([$0], [AC_COMPILE_IFELSE])dnl
+AC_BEFORE([$0], [AC_RUN_IFELSE])dnl
+
+  AC_CHECK_HEADER([minix/config.h], [MINIX=yes], [MINIX=])
+  if test "$MINIX" = yes; then
+    AC_DEFINE([_POSIX_SOURCE], [1],
+      [Define to 1 if you need to in order for `stat' and other
+       things to work.])
+    AC_DEFINE([_POSIX_1_SOURCE], [2],
+      [Define to 2 if the system does not provide POSIX.1 features
+       except with this defined.])
+    AC_DEFINE([_MINIX], [1],
+      [Define to 1 if on MINIX.])
+  fi
 
   AH_VERBATIM([__EXTENSIONS__],
-[/* Enable extensions on Solaris.  */
-#ifndef __EXTENSIONS__
-# undef __EXTENSIONS__
+[/* Enable extensions on AIX 3, Interix.  */
+#ifndef _ALL_SOURCE
+# undef _ALL_SOURCE
 #endif
+/* Enable GNU extensions on systems that have them.  */
+#ifndef _GNU_SOURCE
+# undef _GNU_SOURCE
+#endif
+/* Enable threading extensions on Solaris.  */
 #ifndef _POSIX_PTHREAD_SEMANTICS
 # undef _POSIX_PTHREAD_SEMANTICS
 #endif
+/* Enable extensions on HP NonStop.  */
 #ifndef _TANDEM_SOURCE
 # undef _TANDEM_SOURCE
-#endif])
+#endif
+/* Enable general extensions on Solaris.  */
+#ifndef __EXTENSIONS__
+# undef __EXTENSIONS__
+#endif
+])
   AC_CACHE_CHECK([whether it is safe to define __EXTENSIONS__],
     [ac_cv_safe_to_define___extensions__],
     [AC_COMPILE_IFELSE(
-       [AC_LANG_PROGRAM([
+       [AC_LANG_PROGRAM([[
 #	  define __EXTENSIONS__ 1
-	  AC_INCLUDES_DEFAULT])],
+	  ]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([_ALL_SOURCE])
+  AC_DEFINE([_GNU_SOURCE])
   AC_DEFINE([_POSIX_PTHREAD_SEMANTICS])
   AC_DEFINE([_TANDEM_SOURCE])
-])
+])# AC_USE_SYSTEM_EXTENSIONS
 
 # gl_USE_SYSTEM_EXTENSIONS
 # ------------------------