Remove limitation on DebugIR that made it require existing debug metadata.
- Build debug metadata for 'bare' Modules using DIBuilder
- DebugIR can be constructed to generate an IR file (to be seen by a debugger)
  or not in cases where the user already has an IR file on disk.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185193 91177308-0d34-0410-b5e6-96231b3b80d8