cmd/api: reduce stutter in runtime type stubs

LGTM=khr
R=khr
CC=dvyukov, golang-codereviews
https://golang.org/cl/132770044

src/cmd/api/goapi.go

@@ -378,10 +378,12 @@ func (w *Walker) parseFile(dir, file string) (*ast.File, error) {
 	}
 	if w.context != nil && file == fmt.Sprintf("zruntime_defs_%s_%s.go", w.context.GOOS, w.context.GOARCH) {
 		// Just enough to keep the api checker happy.
-		src := "package runtime; type maptype struct{}; type _type struct{}; type alg struct{};" +
-			" type mspan struct{}; type m struct{}; type lock struct{}; type slicetype struct{};" +
-			" type iface struct{}; type eface struct{}; type interfacetype struct{}; type itab struct{};" +
-			" type mcache struct{}; type bucket struct{}; type sudog struct{}; type g struct{}"
+		src := "package runtime; type (" +
+			" maptype struct{}; _type struct{}; alg struct{};" +
+			" mspan struct{}; m struct{}; lock struct{}; slicetype struct{};" +
+			" iface struct{}; eface struct{}; interfacetype struct{}; itab struct{};" +
+			" mcache struct{}; bucket struct{}; sudog struct{}; g struct{};" +
+			")"
 		f, err = parser.ParseFile(fset, filename, src, 0)
 		if err != nil {
 			log.Fatalf("incorrect generated file: %s", err)