process: maintain constructor descriptor

Use the original property descriptor instead of just taking the value,
which would, by default, be non-writable and non-configurable.

PR-URL: https://github.com/nodejs/node/pull/9306


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>