[babl] babl: s/__GNU_SOURCE/_GNU_SOURCE/ fixing issue #59

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 44bd70feafddf53b476acaa4093dee8c8668a599
Author: Øyvind Kolås <pippin gimp org>
Date:   Sun Jun 7 18:47:57 2020 +0200

    babl: s/__GNU_SOURCE/_GNU_SOURCE/ fixing issue #59

 babl/babl-mutex.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/babl/babl-mutex.h b/babl/babl-mutex.h
index 77cb79870..f5dcefb82 100644
--- a/babl/babl-mutex.h
+++ b/babl/babl-mutex.h
@@ -20,7 +20,7 @@
 #define _BABL_MUTEX_H
 
 #ifndef _WIN32
-#define __GNU_SOURCE 1
+#define _GNU_SOURCE 1
 #include <pthread.h>
 #else
 #include <windows.h>