[llvm] [llvm][DebugInfo] [llvm][DebugInfo] Add 'sourceLanguageVersion' field support to DICompileUnit (PR #162632)

[Michael Buch via llvm-commits]

Michael137 wrote:

> ```
> ls llvm/test/Bitcode/*upgrade*
> ```

Added. Turns out there were a couple already there that exercise this upgrade codepath, but I added a dedicated test just in case.

https://github.com/llvm/llvm-project/pull/162632