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

[Alfie Richards via llvm-commits]

AlfieRichardsArm wrote:

Hi @dyung,
This is likely a regression that there weren't tests for. I will look into this urgently tomorrow.
Alfie

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