swift234

Implement partially dead argument elimination.

This change includes an option on how IsLive is defined/computed. the ProjectionTree
can now choose to ignore epilogue releases and mark a node as dead if its only non-debug
user is epilogue release.

It can also mark a node as alive even its only user is epilogue release as before.

Imagine a case where one passes in an array and not access its owner
besides to release it. In such a case, we *do* want to be able to eliminate
that argument even though there is a release in the function epilogue.

This will help to get rid of the retain and release pair at the callsite. i.e.
the guaranteed paramter is elimininated.

rdar://21114206