[llvm] [RISCV] Add support for new unprivileged extensions defined in profiles spec (PR #77458)

[Alex Bradbury via llvm-commits]

asb wrote:

> Do we have any existing precedent where we take the liberty of assuming implied extensions?

I don't think so. It doesn't need to block this PR, but it would be good to raise the question about those implications in the profiles repo.

https://github.com/llvm/llvm-project/pull/77458