Pacify gcc -Woverflow more nicely

* src/alloc.c (mark_maybe_pointer): Simplify pacification
of gcc -Woverflow (unknown GCC version).

src/alloc.c

@@ -4764,12 +4764,7 @@ mark_maybe_pointer (void *p, bool symbol_only)
 	 from Emacs source code, it can occur in some cases.  To fix
 	 this problem, the pdumper code should grok non-initial
 	 addresses, as the non-pdumper code does.  */
-#ifdef WIDE_EMACS_INT
-      uintptr_t mask = ~((uintptr_t) 0);
-#else
-      uintptr_t mask = VALMASK;
-#endif
-      void *po = (void *) ((uintptr_t) p & mask);
+      void *po = (void *) ((uintptr_t) p & (uintptr_t) VALMASK);
       char *cp = p;
       char *cpo = po;
       /* Don't use pdumper_object_p_precise here! It doesn't check the