[MS] Warn when shadowing template parameters under -fms-compatibility

Summary:
C++ does not allow shadowing template parameters, but previously we
allowed it under -fms-extensions. Now this behavior is controlled by
-fms-compatibility, and we emit a -Wmicrosoft-template warning when it
happens.

Fixes PR43265

Reviewers: thakis, hans

Subscribers: amccarth, rsmith, STL_MSFT, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67463

llvm-svn: 371753