Move overlay inclusions outside of header protection

Glibc tends to include standard headers with special definitions
that make few declarations or macros visible, this stomps over the
overlay #include_next <> logic.

Based-on-patch-by: Robert Millan <rmh@debian.org>

include/bsd/stdlib.h

@@ -26,13 +26,6 @@
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef LIBBSD_STDLIB_H
-#define LIBBSD_STDLIB_H
-
-#include <sys/cdefs.h>
-#include <sys/stat.h>
-#include <stdint.h>
-
 #ifdef LIBBSD_OVERLAY
 #include_next <stdlib.h>
 #else
@@ -46,6 +39,13 @@
 #include <bsd/libutil.h>
 #endif
 
+#ifndef LIBBSD_STDLIB_H
+#define LIBBSD_STDLIB_H
+
+#include <sys/cdefs.h>
+#include <sys/stat.h>
+#include <stdint.h>
+
 __BEGIN_DECLS
 u_int32_t arc4random();
 void arc4random_stir();