[clang] [llvm] [Clang] Add `__builtin_stack_address` (PR #148281)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

The backend code looks like what I expect.  Needs a backend regression test for some non-SPARC target.

https://github.com/llvm/llvm-project/pull/148281