[compiler-rt] Revert "[safestack] Various Solaris fixes" (PR #98541)

[Rainer Orth via llvm-commits]

rorth wrote:

I think we should add a prominent comment to `safestack_platform.h` why this is needed despite `sanitizer_common`.

Good thing you didn't revert only partially: with the `RTSanitizerCommon` part gone, every single safestack test would have failed to link on Solaris, breaking both buildbots.

I guess the way forward is to add stub versions of `__sanitizer_internal_memset` etc. that just `abort`: on Linux/x86_64, the test executables still contains undefined references to those, with no definition in sight, so it doesn't seem the are needed.  With PR #98469 modified like this, safestack should be restored on Solaris.

As for PR #98513, I'll have to figure out how to fix `safestack_platform.h` to include what `sanitizer_linux.cpp` does differently for `mmap` and `TgKill`, otherwise the multilib testing patch cannot go in.

https://github.com/llvm/llvm-project/pull/98541