[TypeChecker] NFC: Add a test-case for rdar://problem/62842651

Author: xedin

test/Constraints/rdar62842651.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend -emit-sil -verify %s | %FileCheck %s
+
+class A {}
+class B: A {}
+
+func test<T>(_ type: T.Type) -> T? {
+  fatalError()
+}
+
+// CHECK: [[RESULT:%.*]] = function_ref @$s12rdar628426514testyxSgxmlF
+// CHECK-NEXT: apply [[RESULT]]<B>({{.*}})
+let _: A? = test(B.self)