mingw-w64 currently is lacking the headers for this feature.
Make the include lowercase at the same time. We consistently
use lowercase for windows header includes, as windows itself is
case insensitive, the SDK headers (in general, not necessarily
considering this particular header) aren't consistent among themselves
about what the proper canonical capitalization for headers are,
and MinGW uses all lowercase names for the headers (as it is often
used on case sensitive filesystems).
In case mingw-w64 later gets this header, we can revert this
(but keep the include lowercased).
Differential Revision: https://reviews.llvm.org/D58765
llvm-svn: 355236
05394af3ff