Make the occurrence analyser track preInlineUnconditionally

Make the occurrence analyser track preInlineUnconditionally

This fixes a somewhat obscure situation in which an
over-optimistic use of "occurs once" led to an infinite
sequence of simplifier iterations.  Se Note [Cascading inlines]
for the details.

This showed up when compiling rather large DPH programs, which
run lots of iterations of the simplifier, which in turn made
compilation take much longer than necessary.