IR: ConstProp potentially incorrect mask
https://github.com/FEX-Emu/FEX/blob/main/External/FEXCore/Source/Interface/IR/Passes/ConstProp.cpp#L358

This mask value is set but never used. Looks like it should be used in place of `imm` on line `auto newArg = RemoveUselessMasking(IREmit, IROp->Args[i], imm);` but needs to be investigated.