build: gh850 support msys
build: gh850 support msys

When we detect msys as a platform, we should behave as if it is
a Win32 system.  Otherwise, the build will be broken in the msys
shell.

Change-Id: I088f954ca968c9ce21bc7bbe7bfaa7732dd82a73

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools