[clang] ObjcRuntime.h: Add mips64, aarch64, and riscv64 to non-legacy dispatch (PR #76694)

[David Chisnall via cfe-commits]

davidchisnall wrote:

> I assume we can split the test into two parts:
> 
> 1. Checking if the driver correctly sets `-fobjc-dispatch-method`
> 2. Checking if frontend emits `objc_msgSend`

Ah, I forgot that was how it propagated. I think we only need the driver tests, there should be existing checks for the dispatch-method thing.

https://github.com/llvm/llvm-project/pull/76694