enolan authored Sep 25, 2017 and Ben Gamari committed Sep 25, 2017

Prior to this commit, worker OS thread were renamed to "ghc_worker" when
spawned. This was annoying when reading debugging messages that print
the process name because it doesn't tell you *which* Haskell program is
generating the message.

This commit changes it to "original_process_name:w", truncating the
original name to fit in the kernel buffer if neccesary.

Test Plan: ./validate

Reviewers: austin, bgamari, erikd, simonmar

Reviewed By: bgamari

Subscribers: Phyx, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D4001