support operator keywords used in Windows SDK

support operator keywords used in Windows SDK

to support operator keywords used in Windows SDK, alter token type when
seen in system headers

Hello, I submitted D33505 to address this problem, but the
proposal was rejected as too big a hammer.
This change will allow clang to parse the WindowsSDK header <query.h>
which uses the operator name "or" as a field name. Treat cpp operator
keywords as ordinary identifiers inside the Microsoft headers, but
treat them as usual in the user's program.

Original Submitter: Melanie Blower (mibintc)

Differential Revision: https://reviews.llvm.org/D33782

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@305087 91177308-0d34-0410-b5e6-96231b3b80d8