the old AC_USE_SYSTEM_EXTENSIONS won't work with AC_GNU_SOURCE

against 4.2.31
07/08/2010 - qhe

diff --git a/gnulib/m4/extensions.m4 b/gnulib/m4/extensions.m4
index 143a9e5..0f27ceb 100644
--- a/gnulib/m4/extensions.m4
+++ b/gnulib/m4/extensions.m4
@@ -12,44 +12,6 @@
 # enough in this area it's likely we'll need to redefine
 # AC_USE_SYSTEM_EXTENSIONS for quite some time.
 
-# AC_USE_SYSTEM_EXTENSIONS
-# ------------------------
-# Enable extensions on systems that normally disable them,
-# typically due to standards-conformance issues.
-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])
-
-  AH_VERBATIM([__EXTENSIONS__],
-[/* Enable extensions on Solaris.  */
-#ifndef __EXTENSIONS__
-# undef __EXTENSIONS__
-#endif
-#ifndef _POSIX_PTHREAD_SEMANTICS
-# undef _POSIX_PTHREAD_SEMANTICS
-#endif
-#ifndef _TANDEM_SOURCE
-# undef _TANDEM_SOURCE
-#endif])
-  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])
-  AC_DEFINE([_TANDEM_SOURCE])
-])
-
 # gl_USE_SYSTEM_EXTENSIONS
 # ------------------------
 # Enable extensions on systems that normally disable them,
