[llvm] [ARM][TableGen][MC] Change the ARM mnemonic operands to be optional for ASM parsing (PR #83436)

[Peter Smith via llvm-commits]

smithp35 wrote:

Yes, all I've done is just plug the example on GCC. If we're lucky there will be a comment in the source code or commit message for GCC, or clang saying that it has copied GCC.

There will be a limit to what we can do, sometimes there won't be anything written down that can be easily found.

https://github.com/llvm/llvm-project/pull/83436