Tamar Christina authored Feb 23, 2017 and Ben Gamari committed Feb 26, 2017

The GCC Bindists that we use compile with `pthread` enabled by default.
This means that on every link the dll is passed as a dependency by the
driver. Lots of packages depend on it but the runtime linker doesn't
provide it by default making compiled code work but not interpreted.

Following D3028 `pthreads` would be provided by default ONLY when linked
dynamicly, which we don't support yet (See D2592). Until this is the
case we need to manually provide `libpthreads`.

Test Plan: ./validate

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D3155