GHC_STAGE1 isn't defined, use other form.

Authored by ezyang on Mar 10 2017, 4:33 PM.

Description

GHC_STAGE1 isn't defined, use other form.

Summary:
I don't really know why this stopped working for me, but it
did on a recent clean. I don't know if this is right but
it solved the problem for me.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: bgamari, austin

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3318