[clang] [clang][Sema] Deprecate `global`/`unknown` in `lifetime_capture_by` (PR #196635)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I guess we should add an explicit way to suppress these warnings, to handle cases where it's a third-party dependency whose code you don't control.

The explicit way to do that is `-Wno-deprecated-attributes`; we don't make carve-outs for other deprecated attributes, and I don't think anything is different here.

https://github.com/llvm/llvm-project/pull/196635