[clang] [Clang] Add "extend lifetime" flags and release note (PR #110000)

[Stephen Tozer via cfe-commits]

SLTozer wrote:

This patch has been changed as a result of some other patches that have removed the need for the attribute that this patch once added. Since this patch does not emit fake uses (the actual emission of fake uses is added in the [next patch](https://github.com/llvm/llvm-project/pull/110102)), that leaves this patch in the awkward position of adding flags and a release note but not actually doing anything. I'd prefer to leave this patch separate though, because the next patch is already tricky to review - adding more to that patch would probably slow things down a bit.

https://github.com/llvm/llvm-project/pull/110000