PR15149: crash when printing debug info metadata containing an invalid language spec

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174304 91177308-0d34-0410-b5e6-96231b3b80d8
[DebugInfo] remove more node indirection (this time from the subprogram's variable lists)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174305 91177308-0d34-0410-b5e6-96231b3b80d8