C1: Casts should not be eliminated for interface types

From the review for JDK-8200167, Vladimir writes:

src/hotspot/share/c1/c1_Canonicalizer.cpp
...
 void Canonicalizer::do_CheckCast (CheckCast* x) {
- if (x->klass()->is_loaded()) {
+ if (x->klass()->is_loaded() && !x->is_invokespecial_receiver_check())

It seems like it's not something specific to invokespecial, but a generic problem in how interface casts are handled in C1: it's not correct to eliminate the cast if obj->declared_type() is an interface. I assume that's what happens in your case. FTR I'm fine with handling it separately.