5218 posix definition of NULL
correct unistd.h and iso/stddef_iso.h
update gate source affected

@@ -233,11 +233,11 @@
 
         if (fwd != (char *) NULL) {
             if (cl != (cr = wcsrchr(n, (wchar_t)'!'))) {
                 /*  more than one ! */
                 wcsncpy(tmpbuf, cl+1, cr-cl-1);
-                tmpbuf[cr-cl-1] = NULL;
+                tmpbuf[cr-cl-1] = L'\0';
                 (void) wcstombs(fwd, tmpbuf, MAXFULLNAME);
             }
         } else {
             cr = cl;
         }