[clang] [clang][LoongArch] Enable -fasynchronous-unwind-tables by default on Linux (PR #94711)

[Fangrui Song via cfe-commits]

MaskRay wrote:

`.eh_frame` for non-C++-exception unwinding is pretty bad... As a new architecture, you can avoid doing it...

https://ubuntu.com/blog/ubuntu-performance-engineering-with-frame-pointers-by-default
https://www.brendangregg.com/blog/2024-03-17/the-return-of-the-frame-pointers.html

https://github.com/llvm/llvm-project/pull/94711