improve a test to cover ~Copyable

Author: kavon

test/SILOptimizer/moveonly_class_inits_end_to_end.swift

@@ -3,6 +3,8 @@
 // A test that makes sure end to end in a copyable class containing a
 // non-copyable type, in the init, we only have a single destroy_addr.
 
+
+// CHECK: public struct MO : ~Copyable {
 public struct MO : ~Copyable {
   var x: Int8 = 0
   deinit { print("destroyed MO") }