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

[Hugo Melder via cfe-commits]

hmelder wrote:

> A lot of formatting changes seem to have crept into unrelated bits of the code, please can you revert them? You can use > the clang-format-diff script to format only the bits that you’ve changed.

Done. Sorry for the messy commit history.

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