unshare02: define _GNU_SOURCE

This fixes unshare() being undeclared when building for Android

Signed-off-by: Steven Jackson <sj@oscode.net>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
diff --git a/testcases/kernel/syscalls/unshare/unshare02.c b/testcases/kernel/syscalls/unshare/unshare02.c
index d3e303e..9221f92 100644
--- a/testcases/kernel/syscalls/unshare/unshare02.c
+++ b/testcases/kernel/syscalls/unshare/unshare02.c
@@ -38,6 +38,8 @@
 /*	      Manas Kumar Nayak maknayak@in.ibm.com>			*/
 /******************************************************************************/
 
+#define _GNU_SOURCE
+
 #include <stdio.h>
 #include <sys/wait.h>
 #include <sys/types.h>