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

[Thurston Dang via llvm-commits]

thurstond wrote:

> > For 2., since __asan_disable_fake_stack()/__asan_enable_fake_stack() is a runtime API, it is debatable why it can't
> 
> The point of '=2' is to change Asan pass to generate code which does not check for nullptr.
> 
> Regarding documentation, In this header yes, in Clang docs, better not yet.

By "For 2.", I was referring to bullet point 2 (sorry for the ambiguity):

2. compiled with "runtime", ASAN_OPTIONS=detect_stack_use_after_return=0: fake stack is always off

Why can't this be overridden by  `__asan_disable_fake_stack()`/`__asan_enable_fake_stack()`?

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