[llvm] [RISC-V][MC] Accept an absolute variable value as a CSR number (PR #67377)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

I mean, if GNU as accepts this then I guess so should we, but why can't we also make riscv-arch-test just use the preprocessor like a normal project?

https://github.com/llvm/llvm-project/pull/67377