Some host fail on `assert (!"foo")', which expands to

((!"foo") ? (void)0 : __assert("!"foo."", __FILE__, __LINE__))
Reported by Nelson Beebee.
* src/output.c, src/vcg.c: Replace `assert (!"it succeeded")' with
`#define it_succeeded 0' and `assert (it_succeeded)'.

src/output.c

@@ -978,8 +978,8 @@ pack_vector (int vector)
 	  return j;
 	}
     }
-
-  assert (!"pack_vector");
+#define pack_vector_succeeded 0
+  assert (pack_vector_succeeded);
   return 0;
 }