[libc] (reland #117503) Implement process_mrelease (#117851)

This PR implements process_mrelease.
A previous PR was merged #117503, but failed on merge due to an issue in
the tests. Namely the failing tests were comparing against return type
as opposed to errno. This is fixed in this PR.

GitOrigin-RevId: d2b482b0efd1d523852c9add8ed6b2035ce1acd9
12 files changed