[clang] [RISCV] Add canonical ISA string as Module metadata in IR. (PR #80760)

[Philip Reames via cfe-commits]

preames wrote:

I agree with @asb's framing above.  Assuming this doesn't commit us to something which is hard to forward version for some reason, I support addressing this in a target specific manner for the moment. 

https://github.com/llvm/llvm-project/pull/80760