Gc.relocate insertion for WinEH

[JosephTremoulet]

Statepoint insertion adds explicit gc.relocate intrinsic calls to reflect retrieving the updated value of a GC pointer across a statepoint. When the statepoint is an invoke that may throw, gc.relocate calls are (currently) needed on both the normal-return path and on the exception path. The current code handles both cases, but only handles the exception path for landingpad-style EH. We'll need to update that to handle funclet-style EH (catchpad/cleanuppad) EH as well.