[llvm] [RISCV][MC] Pass MCSubtargetInfo down to shouldForceRelocation and evaluateTargetFixup. (PR #73721)

[Fangrui Song via llvm-commits]

MaskRay wrote:

There should be a `llc -filetype=obj %s` test (no `-mattr=+relax`) where a function has a `"target-features"` including `+relax`.
I added `llvm/test/CodeGen/RISCV/relax-per-target-feature.ll`, which should be adjusted by this patch.

https://github.com/llvm/llvm-project/pull/73721