[clang] [Clang] Add GCC's __builtin_stack_address() to Clang. (PR #121332)

[Nikita Popov via cfe-commits]

https://github.com/nikic commented:

Other builtins like __builtin_frame_address and __builtin_return_address map onto an llvm intrinsic like llvm.frameaddress or llvm.returnaddress. What's the reason for not following this design for __builtin_stack_address?

https://github.com/llvm/llvm-project/pull/121332