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

[David Chisnall via cfe-commits]

davidchisnall wrote:

No, clang tests are not executable.  This test is the right approximate shape:


https://github.com/llvm/llvm-project/blob/a3e8e86fb6ad27fe070bb2c0f54a1c697c665f13/clang/test/CodeGenObjC/messages.m#L18

The RUN line invokes clang in a few different configurations (you want to invoke it with the `-fobjc-runtime=gnustep-{version}` flag and the correct triples and then check that we get either `objc_msgSend` or `objc_msg_lookup`, depending on whether `objc_msgSend` is expected to be supported in that configuration.

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