Revert "Recommit r212203: Don't try to construct debug LexicalScopes hierarchy for functions that do not have top level debug information."

This reverts commit r212649 while I investigate/reduce/etc PR20367.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213581 91177308-0d34-0410-b5e6-96231b3b80d8