[vte] build: Remove manual define of _GNU_SOURCE

[Egmont Koblinger <egmontkob src gnome org>]

commit 6acfa59dfcceef65c1f7e3570db37ab245f049c4
Author: Egmont Koblinger <egmont gmail com>
Date:   Sun Oct 15 22:36:38 2017 +0200

    build: Remove manual define of _GNU_SOURCE
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788476#c18

 src/vteutils.cc |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)
---
diff --git a/src/vteutils.cc b/src/vteutils.cc
index e683375..154b854 100644
--- a/src/vteutils.cc
+++ b/src/vteutils.cc
@@ -18,10 +18,6 @@
 
 #include "config.h"
 
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE /* for O_TMPFILE */
-#endif
-
 #include "vteutils.h"
 
 #include <fcntl.h>