Relocatable GHC

GHC and the binary distribution that's produced is
not relocatable outside of Windows.  This diff tries to
address this for at least Linux and macOS.

Reviewers: austin, hvr, bgamari, erikd, goldfire, Phyx

Reviewed By: bgamari

Subscribers: duog, rwbarton, thomie, erikd

Differential Revision: https://phabricator.haskell.org/D4121