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

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> Fixes the same issue on riscv/musl, thanks.

How exactly it fixes riscv if changed code is  __powerpc64__ only?

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