Reapply r180982 with repaired logic and an additional testcase.

Un-break the gdb buildbot.
- Use the debug location of the return expression for the cleanup code
  if the return expression is trivially evaluatable, regardless of the
  number of stop points in the function.
- Ensure that any EH code in the cleanup still gets the line number of
  the closing } of the lexical scope.
- Added a testcase with EH in the cleanup.

rdar://problem/13442648