Moritz Angermann authored Jun 25, 2016 and Tamar Christina committed Jun 25, 2016

Summary:
Commit 90538d86, seems to have broken static linking.
The introduction of `argFixup` in `runLink` rearranges libs, and considers
anything with an `-l` prefix or `.a` suffix a lib, which fails for libs that are
just being linked together (e.g. `-o lib.a`).

The proposed solution explicitly checks for the existance of the `-o` flag.

Reviewers: rwbarton, erikd, Phyx, bgamari, austin

Reviewed By: Phyx

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2362