[clang] [llvm] [RISCV] Add the Sha extension (PR #113820)

[Sam Elliott via cfe-commits]

lenary wrote:

> I haven't made it so if you enable all extensions that constitute Sha, Sha is implied.

Great! I think it's most clear if we have "extensions only require things they are made up of" (i.e. all the implications/requirements point to earlier/lesser extensions) and "profiles are how you enforce a lower bound on the set of extensions present" we're going to be in a much more sustainable situation than other architectures where they try to use the presence of a combination of other extensions to lower-bound the set of present extensions. 

https://github.com/llvm/llvm-project/pull/113820