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/err.h

@@ -25,6 +25,12 @@
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#ifdef LIBBSD_OVERLAY
+#include_next <err.h>
+#else
+#include <err.h>
+#endif
+
 #ifndef LIBBSD_ERR_H
 #define LIBBSD_ERR_H
 
@@ -32,12 +38,6 @@
 
 #include <stdarg.h>
 
-#ifdef LIBBSD_OVERLAY
-#include_next <err.h>
-#else
-#include <err.h>
-#endif
-
 __BEGIN_DECLS
 extern void warnc (int code, const char *format, ...);
 extern void vwarnc (int code, const char *format, va_list ap);