Add missing comma in 'libdw' configure check
Add missing comma in 'libdw' configure check

Fix a bug from cb882fc993b4972f7f212b291229ef9e9ade0af9. Without the
comma, all non-diverging codepaths set 'UseLibdw=NO'.

Reviewers: bgamari, nh2

Reviewed By: nh2

Subscribers: rwbarton, erikd, carter

GHC Trac Issues: #15968

Differential Revision: https://phabricator.haskell.org/D5459

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc