this is GNU source

libc/misc/pthread/no-tsd.c

@@ -17,6 +17,7 @@
    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.  */
 
+#define _GNU_SOURCE
 #include <bits/libc-tsd.h>
 
 /* This file provides uinitialized (common) definitions for the

libc/misc/pthread/weaks.c

@@ -17,6 +17,7 @@
    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.  */
 
+#define _GNU_SOURCE
 #include <errno.h>
 #include <limits.h>
 #include <stdlib.h>