swift234

Handle dead functions in CallerAnalysis.

Add an invalidateAnalysisForDeadFunction API. This API calls the invalidateAnalysis
by default unless overriden by analysis pass themselves. This API passes the extra
information that this function is dead and going to be removed from the module.

CallerAnalysis overrides this API and only invalidate caller/callee relations but
does not push this into the recompute list.

We also considered the possibility of keeping a computed list, instead of recompute
list but that would introduce a O(n^2) complexity as every time we try to complete
the computed list, we need to walk over all the functions that currently exist in the
module to make sure the computed list is complete.

I feel eventually we can do a handleDeleteNotification for function deletion and we
wont need the API added in this change.