clang-cl: Don't warn for unused private fields when encountering a late parsed template member

Summary: This fixes PR21235.

Test Plan: Includes an automated test.

Reviewers: hansw

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5718

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219551 91177308-0d34-0410-b5e6-96231b3b80d8
[modules] When instantiating a class member, don't expect to find the previous
declaration in the instantiation if the previous declaration came from another
definition of the class template that got merged into the pattern definition.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219552 91177308-0d34-0410-b5e6-96231b3b80d8