clang-cl: Warn when a /TC or /TP argument is unused

Test Plan: The patch includes a test case.

Reviewers: hansw

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5338

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217710 91177308-0d34-0410-b5e6-96231b3b80d8