tools build failure on Linux (and fix)

[coypu]

I'm compiling NetBSD-current (tools) on Linux.
I needed to use the following patch because external/gpl3/gcc.old/dist/gcc
doesn't use RCSID anywhere and Linux doesn't define __RCSID by default.

--- a/external/gpl3/gcc.old/dist/gcc/regsub.c
+++ b/external/gpl3/gcc.old/dist/gcc/regsub.c
@@ -29,7 +29,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: regsub.c,v 1.1 2016/01/09 02:00:14 christos Exp $");

 #include <sys/param.h>