Add support for custom alias analysis pass pipeline in new pm

[wsmoses]

No description provided.

[maleadt]

There's PassBuilder::parseAAPipeline to call into. I'm not entirely sure what's the best design here, either having the default pipeline parser detect an aa(...) grouping, or by adding a wholly separate AA pipeline like opt does with aa-pipeline. Should probably best discuss this with upstream first.

I'm also not sure how pressing this is, i.e., if we're currently running without AA at all, or what the default is.