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

[Saleem Abdulrasool via llvm-commits]

compnerd wrote:

I think that we should consider the alternative idea as well - generating the relocations to enable relaxations if `-mrelax` is set.

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