[clang] [clang] Add __builtin_start_object_lifetime builtin. (PR #82776)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This would also need a release note I believe. I don't have the codegen expertise to review this with high confidence, but it looks right to me.

https://github.com/llvm/llvm-project/pull/82776