[clang] [Clang] Enable -fextend-lifetimes at -Og (PR #118026)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Since the option has been renamed to `-fextend-variable-liveness`, I think you want to edit this title and the description to reflect the naming change as well. I wanted to check the status the effort and I tried `git log --grep fextend-lifetimes` but found nothing, then I realized that the option has been renamed :)

https://github.com/llvm/llvm-project/pull/118026