[MVT] Eliminate redundant value type allocations

C2 currently creates two allocations in the following case:

        // Create value type and force allocation
        MyValue3 vt = MyValue3.create();
        va[0] = vt;
        val77 = vt;
        vt.verify(val77);

        // Value type is now allocated, make a copy and force allocation.
        MyValue3 copy = MyValue3.setC(vt, vt.c);
        va[0] = copy;

But because copy is equal to vt, C2 should eliminate this redundant allocation.