AOSP: Android: consolidate addition of include/mingw/

To match what the autotools-based build system does now, always add
include/mingw/ to the include path on Windows.  I don't think this makes
a real difference anywhere, but this is much simpler.

Change-Id: I92fdaf3e58029dfca3187af928d943270b2a2109
From AOSP commit: c9aa74eac41f8feeabb2321383161c7cf92cb49b
6 files changed