[glib] configure: Use AC_USE_SYSTEM_EXTENSIONS

[Colin Walters <walters src gnome org>]

commit d2bb019533bbcbd1cee3891822ac7ba6ff55ad3d
Author: Colin Walters <walters verbum org>
Date:   Fri Jul 26 12:39:51 2013 +0100

    configure: Use AC_USE_SYSTEM_EXTENSIONS
    
    ...instead of detecting glibc and using _GNU_SOURCE manually.  This
    should fix the build when using glibc-emulating libraries; we can
    defer portability work to autoconf.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=684123

 configure.ac |    6 +-----
 1 files changed, 1 insertions(+), 5 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index d309f28..9443709 100644
--- a/configure.ac
+++ b/configure.ac
@@ -111,6 +111,7 @@ AC_SUBST(LT_CURRENT_MINUS_AGE)
 dnl Checks for programs.
 AC_PROG_CC
 AC_PROG_CPP
+AC_USE_SYSTEM_EXTENSIONS
 
 AM_CONDITIONAL(HAVE_GCC, [test "$GCC" = "yes"])
 
@@ -231,11 +232,6 @@ if test "x$glib_have_cocoa" = "xyes"; then
   LDFLAGS="$LDFLAGS -Wl,-framework,Foundation"
 fi
 
-gl_GLIBC21
-AS_IF([test "x$GLIBC21" = "xyes"], [
-  AC_DEFINE([_GNU_SOURCE], 1, [Make all glibc extensions visible])
-])
-
 dnl declare --enable-* args and collect ac_help strings
 AC_ARG_ENABLE(debug,
               AS_HELP_STRING([--enable-debug=@<:@no/minimum/yes@:>@],