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

@@ -478,11 +478,11 @@
                         return(FALSE);
                 }
 
         ASSERT(len >= BUFSIZ, "BUFFER TOO SMALL", "getsysline", 0);
         for(;;) {
-                while (getaline(fsystems, buf) != NULL)
+                while (getaline(fsystems, buf) != 0)
                     if ((*buf != '#') && (*buf != ' ') &&
                         (*buf != '\t') && (*buf != '\n')) {
                         (void) _uu_resetlocale(LC_ALL, prev);
                         return(TRUE);
                 }