Alp Mestanogullari authored May 12, 2018 and Tamar Christina committed May 12, 2018

Summary:
This requires adding an `sToolDir :: Maybe FilePath` field to Settings, since
compilerInfo is pure and therefore needs to have all the information
available in the DynFlags.

This should fix #15101 and #15107.

Test Plan: ./validate --fast

Reviewers: Phyx, bgamari

Reviewed By: Phyx

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #15101, #15107

Differential Revision: https://phabricator.haskell.org/D4686