Implement template support for CapturedStmt

- Sema tests added and CodeGen tests are pending

Differential Revision: http://llvm-reviews.chandlerc.com/D728



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181101 91177308-0d34-0410-b5e6-96231b3b80d8