Crucible/LLVM: Group argument equality assertions in override matching

[langston-barrett]

Crucible/LLVM currently matches arguments for overrides by collecting a bunch of assertions (from methodSpecHandler_prestate):

       xs <- liftIO (zipWithM aux expectedArgTypes (assignmentToList args))
       sequence_ [ matchArg opts sc cc cs PreState x y z | (x, y, z) <- xs]

The matchArg function is in an OverrideState state monad, and so doesn't return the assertions it makes. We're losing granularity here: when the call to matchArg is made, we know that the added assertions are related to an equality condition for the override's arguments, but after the call we have no understanding of where they came from.

If we keep track of which argument equality these assertions come from, we can later report that more meaningfully/at a higher level to the user.