[clang] [Driver] Don't default to -mrelax-all for non-RISCV -O0 (PR #90013)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> .text
>         b dest    // b.n 2-byte branch
>         b dest2  // b.w 4-byte branch
>         nop
> dest:
>         nop
>         .space 2048
> dest2:
>         nop

Thanks for checking. Confirmed no impact to ARM because `llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp:createELFStreamer` ignores `RelaxAll` parameter and passes `false`.

https://github.com/llvm/llvm-project/pull/90013