misc/cgo/errors: test that the Go rune type is not identical to C.int

rune has a well-defined size, but C.int is implementation-specified.
Using one as the other should require an explicit conversion.

updates #13467

Change-Id: I53ab2478427dca790efdcc197f6b8d9fbfbd1847
Reviewed-on: https://go-review.googlesource.com/63730Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/errors/errors_test.go

@@ -114,6 +114,7 @@ func TestReportsTypeErrors(t *testing.T) {
 		"issue11097b.go",
 		"issue13129.go",
 		"issue13423.go",
+		"issue13467.go",
 		"issue13635.go",
 		"issue13830.go",
 		"issue16116.go",

misc/cgo/errors/src/issue13467.go

+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+/*
+static int transform(int x) { return x; }
+*/
+import "C"
+
+func F() {
+	var x rune = '✈'
+	var _ rune = C.transform(x) // ERROR HERE: C\.int
+}