It looks like the performance regressions w/o global method cache are
because rb_funcall and friends do not have call info, so they don't
hit the inline cache.  So perhaps we should just add a call info-aware
version of rb_funcall-like functions so we can just use inline cache
everywhere.

I'm pretty sure ko1 already knows that, but I just discovered it :x
tmm1: what do you think?