v8: fix build errors with g++ 7

This is a local patch because upstream fixed it differently by moving
large chunks of code out of objects.h.  We cannot easily back-port
those changes due to their size and invasiveness.

Fixes: https://github.com/nodejs/node/issues/10388
PR-URL: https://github.com/nodejs/node/pull/12392


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>