Add an overload of getLastArgNoClaim taking two OptSpecifiers.

Summary: This will be used in clang.

Test Plan: Will be tested on the clang side.

Reviewers: hansw

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5337

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217702 91177308-0d34-0410-b5e6-96231b3b80d8