Chris Smith authored Nov 17, 2018 and Krzysztof Gogolewski committed Nov 17, 2018

Summary:
The effect of this change is that -main-is changes the default
export list for the main module, but does not apply the same
change to non-main modules.  This fixes some cases where -main-is
was used to wrap a module that expected that default behavior
(exporting `main`, even when that wasn't the main entry point
name).

Reviewers: mpickering, monoidal, bgamari

Subscribers: rwbarton, carter

GHC Trac Issues: #13704, #15702

Differential Revision: https://phabricator.haskell.org/D5322