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

[Richard Smith via cfe-commits]

https://github.com/zygoloid commented:

I think this flag name is going to be extremely confusing. "lifetime" is a notion defined formally by the C++ language standard, and "lifetime extension" is again a process defined in C++ with a specific meaning. Those meanings have nothing to do with what these flags control.

Please consider alternative names for this flag that make it clear that it's not talking about changing language semantics, just how code is lowered. Maybe `-fextend-live-ranges` or `-fkeep-alive` or something like that? (Maybe even something that mentions debugging as the intended use case, as opposed to, say, supporting stack-walking GC?)

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