remove AC_USE_SYSTEM_EXTENSIONS to fix the autoconf error "AC_REQUIRE: circular
dependency of AC_GNU_SOURCE"

Signed-off-by: Zhai Edwin <edwin.zhai@intel.com>

Upstream-Status: Inappropriate [licensing]

Index: gzip-1.3.12/m4/extensions.m4
===================================================================
--- gzip-1.3.12.orig/m4/extensions.m4	2010-08-16 14:18:16.000000000 +0800
+++ gzip-1.3.12/m4/extensions.m4	2010-08-16 14:21:54.000000000 +0800
@@ -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,