[llvm] [CHERI] Add enum values and LL parse/print support for CHERI calling conventions. (PR #156328)

[Owen Anderson via llvm-commits]

resistor wrote:

> Upstreaming these makes sense but I wonder if this should wait until we have more of the other core infrastructure landed?

I would prefer to upstream things like enum values early, as they're minimally invasive to LLVM and save on merge conflicts for the downstream.

https://github.com/llvm/llvm-project/pull/156328