Ben Gamari authored Apr 04, 2017 and Ben Gamari committed Apr 04, 2017

For reasons unknown `validate` passed `NO_CLEAN_GMP=YES` to
`maintainer-clean`, leaving a stale `gmp.h` which causes the build to
fail in the event that the uses a tree for validating for two different
target platforms. This is quite unexpected, don't do it.

Reviewers: hvr, austin, rwbarton, dfeuer

Reviewed By: dfeuer

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D3409