src: CHECK() for argument overflow in Spawn()

This commit adds checks for overflow to args and env in Spawn().
It seems extremely unlikely that either of these values would
overflow from a valid use case.

Fixes: https://github.com/nodejs/node/issues/15622
PR-URL: https://github.com/nodejs/node/pull/16761


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>