[clang] [Clang] Add fake use emission to Clang with -fextend-lifetimes (PR #110102)

[Stephen Tozer via cfe-commits]

SLTozer wrote:

I've removed the logic that disables this flag at O0 - this has also removed the need for `-disable-O0-optnone` in any tests. Following the prior patch updating this flag to be an `=` flag represented by an enum, the latest commit changes this patch to handle that type. Finally, I've addressed some minor points - renaming `extendLifetimes=>shouldExtendLifetimes`, and making a vaguely-principled choice of `getAllocatedAddress()` vs `getOriginalAllocatedAddress()` (see my comment [above](https://github.com/llvm/llvm-project/pull/110102#discussion_r1882331401)).

https://github.com/llvm/llvm-project/pull/110102