[clang] [llvm] [RISCV] Remove B and Zbc extension from Andes series cpus. (PR #144022)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

Not related to this PR, but I'd like to raise the question here:

For configurable cores, what is the best way to specify the features? `-mcpu` is meant to support the base configuration, but how can we specify the additional optional extensions? Apparently, failing back to `-march` is silly.

My thought is: can we support `-march/-mcpu` where the values can be `{cpu}(_ext)*`? Will such use be problematic?

https://github.com/llvm/llvm-project/pull/144022