Add support for `__builtin_stack_address` builtin. The semantics match
those of GCC's builtin with the same name.
`__builtin_stack_address` returns the starting address of the stack
region that may be used by called functions. It may or may not include
the space used for on-stack arguments passed to a callee (See [GCC
Bug/121013](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121013)).
Fixes#82632.
