Fix to PR16225 (Assert-on-invalid: isa<LabelDecl>(D) && "declaration not instantiated in this scope")

Differential Revision: http://llvm-reviews.chandlerc.com/D920


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188137 91177308-0d34-0410-b5e6-96231b3b80d8