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

[Alexander Richardson via llvm-commits]

arichardson wrote:

> I agree that the ambiguity is not nice. Currently the string name takes precedence, but I notice that there are no tests for this. Will need to check what binutils does.

Sounds good, I'll try to work on adding tests later this week.

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