Fix up some more windows issues.

- Install the proper pthread libraries for Windows builds.
- Install 32-bit windows libraries in lib/ and not lib64/.
- Start trying to build the gold plugin.
- Refactor confusing return values, and fix some formatting.

Bug: http://b/28196329
Test: Ran build.py correctly.
Change-Id: I1db3d167fab80d23ff2af53476f66a4548ace19c