Build on latest glibc.

git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@1520 fd59a12c-fef9-0310-b244-a6a79926bd2f

exec/ipc.c

@@ -32,6 +32,9 @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE 1
+#endif
 #include <pthread.h>
 #include <assert.h>
 #include <pwd.h>