Introduce BootUnfolding, set when unfolding is absent due to hs-boot file.

Authored by ezyang on May 12 2016, 2:47 PM.

Description

Introduce BootUnfolding, set when unfolding is absent due to hs-boot file.

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

Test Plan: validate

Reviewers: simonpj, austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2246