process: properly close file descriptor on exit

This makes sure the file descriptor is closed syncronously on exit
instead of using the asyncronous version which should not be used
on exit.

PR-URL: https://github.com/nodejs/node/pull/24972
Refs: https://github.com/nodejs/node/pull/24965/files#r240770314


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>