[compiler-rt] Add API to temporalily disable usage of ASAN's fake stack (PR #160135)

[Thurston Dang via llvm-commits]

https://github.com/thurstond requested changes to this pull request.

What is the intended interaction of this API with `-mllvm -asan-use-after-return={never,runtime,always}` and `ASAN_OPTIONS=detect_stack_use_after_return={0,1}`? Please update the description and `TestCases/disable_fake_stack.cpp` to clarify.

Also, if the behavior of `__asan_disable_fake_stack()`/`__asan_enable_fake_stack()` depends on those flags, the naming could be confusing.

https://github.com/llvm/llvm-project/pull/160135