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

[Stephen Tozer via cfe-commits]

SLTozer wrote:

> Is this ready to go? I can't recall if we ultimately accepted the RFC.

My interpretation of the RFC is that there was a general acceptance of `-Og = -O1 + -fextend-variable-liveness`, so with the acceptance here I believe this is ready!

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