[compiler-rt] [sanitizer_common] Fix build on ppc64+musl (PR #120036)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> > How exactly it fixes riscv if changed code is **powerpc64** only?
> 
> The change to GetTls in sanitizer_linux_libcdep.cpp.

I see "if" vs "#if".
Thanks!

https://github.com/llvm/llvm-project/pull/120036