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

[Stephen Tozer via cfe-commits]

SLTozer wrote:

I've updated this patch, and made it dependent on a [previous PR](https://github.com/llvm/llvm-project/pull/110000) - the logic for enabling the flag is coupled with code from the earlier PR, and also we now slightly extend the test added in that PR instead of creating a new one.

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