This is no-functional-change-intended, but there's enough churn here that I thought it would be best to do this as a preliminary patch for D38566.
This is repackaging the functionality of D30333 (defer switch-to-lookup-tables) and D35411 (defer folding unconditional branches) with pass parameters rather than a named "latesimplifycfg" pass. Now that we have individual options to control the functionality, we could decouple when these fire (but that's an independent patch if desired). The next planned step would be to add another option bit to disable the sinking transform mentioned in D38566.
As mentioned in D38138, I don't know if it's intentional or oversight that we don't have a "latesimplifycfg" equivalent invocation with the new pass manager pipeline. To make that explicit, I removed the default constructor used by that PM, so we'd be aware that we're always creating an "early" (ie, not fully functional) version of the simplifycfg pass.