Check TargetPlatform instead of HostPlatform for leading underscore
Check TargetPlatform instead of HostPlatform for leading underscore

Reviewers: austin, hvr, rwbarton, bgamari

Reviewed By: rwbarton, bgamari

Subscribers: rwbarton, thomie, erikd

Differential Revision: https://phabricator.haskell.org/D3348

shlevy/ghc,sdiehl/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,shlevy/ghc,sdiehl/ghc,ezyang/ghc