reflect: make types AssignableTo when they share their underlying type

Author: Ben Krieger

src/reflect/type.go

@@ -976,7 +976,7 @@ func (t *rawType) FieldAlign() int {
 // AssignableTo returns whether a value of type t can be assigned to a variable
 // of type u.
 func (t *rawType) AssignableTo(u Type) bool {
-	if u := u.(*rawType); t == u || t.underlying() == u || t == u.underlying() {
+	if t.underlying() == u.(*rawType).underlying() {
 		return true
 	}