Handle predefined expression for a captured statement

- __func__ or __FUNCTION__ returns captured statement's parent
  function name, not the one compiler generated.

Differential Revision: http://llvm-reviews.chandlerc.com/D1491

Reviewed by bkramer



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189219 91177308-0d34-0410-b5e6-96231b3b80d8