[clang] [llvm] [RFC][RISCV] Use the 'B' extension in RISC-V profile definitions (PR #113942)

[Sam Elliott via cfe-commits]

lenary wrote:

I think we shouldn't do this for RVA22, so as not to break existing users of that profile, who may have a toolchain that doesn't support B.

This change makes sense to me for the RV*23 profiles, especially since your change to RVM23 has been accepted.

https://github.com/llvm/llvm-project/pull/113942