babl-mutex: Define _GNU_SOURCE instead of __USE_GNU

__USE_GNU should only be set internally by the libc feature detect macros.
On older Debian-based systems, as used by Heroku cedar-10 stack, this failed
to provide the definition of PTHREAD_MUTEX_RECURSIVE

diff --git a/babl/babl-mutex.h b/babl/babl-mutex.h
index 99fdbaa1c2b6af891d4825826ec94dd46eb1eeea..57154b3471e68d89676032b683132043e43a2fc0 100644 (file)
--- a/babl/babl-mutex.h
+++ b/babl/babl-mutex.h
@@ -20,7 +20,7 @@
 #define _BABL_MUTEX_H
 
 #ifndef _WIN32
-#define __USE_GNU 1
+#define __GNU_SOURCE 1
 #include <pthread.h>
 #else
 #include <windows.h>