[glib] Fix a preprocessor warning with --disable-visibility

[Christian Persch <chpe src gnome org>]

commit 7bb00fd0e8a18b3e20d30053579f002e587dfbbb
Author: Christian Persch <chpe gnome org>
Date:   Sat Jun 19 16:41:25 2010 +0200

    Fix a preprocessor warning with --disable-visibility
    
    Don't redefine DISABLE_VISIBILITY when already building with
    --disable-visibility.

 gthread/tests/1bit-mutex.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gthread/tests/1bit-mutex.c b/gthread/tests/1bit-mutex.c
index dff095c..abb6ddf 100644
--- a/gthread/tests/1bit-mutex.c
+++ b/gthread/tests/1bit-mutex.c
@@ -26,7 +26,9 @@
    */
 
   /* side-step some glib build stuff */
+  #ifndef DISABLE_VISIBILITY
   #define DISABLE_VISIBILITY
+  #endif
   #define GLIB_COMPILATION
 
   /* rebuild gbitlock.c without futex support,