SIFoldOperands::foldInstOperand folds an immediate value into any number
of inline immediates uses, but it was missing uses that could be inline
if the instruction was commuted. The test diffs mostly show cases where
the immediate value 0 can be folded into more than one commuted v_addc
instruction.
Unfortunately this adds more duplication between
isInlineConstantIfFolded and tryAddToFoldList, but there was already
duplication of the mac/mad handling.