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

[Alex Bradbury via llvm-commits]

asb wrote:

I've added the CHECK lines to riscv-profiles.c as spotted by @topperc, and based on the above discussion I think this is now ready to review.

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