Merge changes I1df53a25,Ib89767c4,I4aa88bfb,I1f769355

* changes:
  disabled ccache for OSX debug builds
  _WIN32 and_WIN64 are defined automatically by MinGW 4.8.3
  Enable building Win64 binaries and running unit tests
  Use our prebuilt Mingw64 toolchain to build Win32 binaries.