Add -D_GNU_SOURCE to CFLAGS, else openpty picks the XOPEN variant of fd_set

libutil/Makefile.in

@@ -5,7 +5,7 @@
 # Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
 #
 
-CFLAGS-libutil := -DNOT_IN_libc -DIS_IN_libutil $(SSP_ALL_CFLAGS)
+CFLAGS-libutil := -DNOT_IN_libc -DIS_IN_libutil $(SSP_ALL_CFLAGS) -D_GNU_SOURCE
 
 LDFLAGS-libutil.so := $(LDFLAGS)
 

libutil/openpty.c

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