[gtk+] configure: fix "AC_RUN_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS"

[Ignacio Casal Quinteiro <icq src gnome org>]

commit b480d9c2ed8034fc1d45cc001de3aa19d38ad8c0
Author: Ignacio Casal Quinteiro <icq gnome org>
Date:   Wed Jun 29 15:14:00 2016 +0200

    configure: fix "AC_RUN_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS"

 configure.ac |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 4971ad3..ae38940 100644
--- a/configure.ac
+++ b/configure.ac
@@ -161,6 +161,9 @@ AC_PROG_MKDIR_P
 AC_PROG_INSTALL
 AC_PROG_MAKE_SET
 
+# Define _GNU_SOURCE etc. where appropriate, e.g. for strptime() on glibc
+AC_USE_SYSTEM_EXTENSIONS
+
 # i18n stuff
 AM_GNU_GETTEXT([external])
 AM_GNU_GETTEXT_VERSION([0.19.7])
@@ -208,9 +211,6 @@ case $host in
     ;;
 esac
 
-# Define _GNU_SOURCE etc. where appropriate, e.g. for strptime() on glibc
-AC_USE_SYSTEM_EXTENSIONS
-
 dnl
 dnl Check for a working C++ compiler, but do not bail out, if none is found.
 dnl We use this for an automated test for C++ header correctness.