[compiler-rt] [compiler-rt][common] Only unmap stacks the runtime has actually mapped (PR #179000)

[Paul Kirth via llvm-commits]

ilovepi wrote:

> I am wondering why only Asan use it? On google server side testing we disable this feature.
>
> I assume it's for better stack overflow reporting. Maybe it's not worth it and completely remove use_sigaltstack?
> 

I'm not sure at all. I just noticied that instrumented builds of clang were breaking for me locally. Removal sounds fine to me, but I'm not clear on the motivation of using the alternate signal stack. 

> Patch itself in general is LGTM, but I bet THREADLOCAL will break some platforms, where it needs allocator. Maybe you have to keep pointer in AsanThread.

hmm, maybe. I saw that there's a few THREADLOCAL uses in sanitizer common, so I'd guess they all must have similar handling/problems? I'll take a look a AsanThread, though.

https://github.com/llvm/llvm-project/pull/179000