[llvm] [MC] Teach checkAsmTiedOperandConstraints about optional operands (PR #81381)

[Alfie Richards via llvm-commits]

AlfieRichardsArm wrote:

Ah very nice, presumably this fixes some of the issues I ran into, but looks like better solution than my hack. 
LGTM

https://github.com/llvm/llvm-project/pull/81381