This extends `optimizeCompareInstr` to re-use previous comparison results if the previous comparison was with an immediate that was 1 bigger or smaller. Example:

CMP x, 13 ... CMP x, 12 ; can be removed if we change the SETg SETg ... ; x > 12 changed to `SETge` (x >= 13) removing CMP

Motivation: This often happens because SelectionDAG canonicalization tends to add/subtract 1 often when optimizing for fallthrough blocks. Example for `x > C` the fallthrough optimization switches true/false blocks with `!(x > C)` --> `x <= C` and canonicalization turns this into `x < C + 1`.