Normalize LLDB version parsing on Darwin to handle both Apple Clang and LLVM versions

[Masrepus]

On Darwin, the default version of LLDB is the one shipped with Apple Clang, but it's also possible that someone runs an LLDB version built from the official LLVM sources, which then has the same versioning scheme as Linux builds. This setup is now supported, normalizing the LLVM version to the Apple Clang one if detected, so that other places in the code that rely on Apple Clang versions being used on Darwin continue to function.

[stephen-f0]

Thank you for your contribution.

Looks good to me - We'll probably have to update/expand the list of LLDB->Clang LLDB version mappings in lldb_version_to_clang at some point or come up with a better way of doing this. That is a separate issue though.

[Masrepus]

Thanks!