Revert "Hack in a MinGW target"

This reverts commit 8fa94f4cc1d7e9d34a1908a4d69df52e5d998a20.
Import Oculus SDK 0.2.5 Linux sources
Apply MinGW changes

$ cd LibOVR
$ mingw32-make PLATFORM=MinGW

Conflicts:
	LibOVR/Makefile
	LibOVR/Src/OVR_SensorFusion.cpp