build: avoid compiler warning during configure

There is no need to redefine _GNU_SOURCE in tests that occur after
gl_INIT, since that macro already AC_DEFINE'd it for us.

Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/configure.ac b/configure.ac
index 71c496883c09a3521c3eda5a1ce7382185cfdf37..a2ce97e3d76e4d18bbdf13c555e2c516770d8070 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -638,7 +638,7 @@ if test "$with_libvirtd" = "no" ; then
   with_lxc=no
 fi
 if test "$with_lxc" = "yes" || test "$with_lxc" = "check"; then
-    AC_TRY_LINK([#define _GNU_SOURCE
+    AC_TRY_LINK([
         #include <sched.h>
     ], [
         unshare (1);