[compiler-rt] Reland '[hwasan] Add fixed_shadow_base flag (#73980)' (PR #95445)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> > @fmayer Can you please check the [8b6c034](https://github.com/llvm/llvm-project/commit/8b6c0349b8885e5183d51d98c6d30927b978e842) ?
> 
> Works

Thanks, testing was very helpful! 

https://github.com/llvm/llvm-project/pull/95445