test: add a compilation test that gccgo failed to compile

R=golang-dev, remyoudompheng
CC=golang-dev
https://golang.org/cl/11379044

test/fixedbugs/bug475.go

+// compile
+
+// Copyright 2013 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.
+
+// Variable in enclosing function with same name as field in struct
+// composite literal confused gccgo.
+
+package p
+
+type s1 struct {
+	f *s1
+}
+
+func F() {
+	var f *s1
+	_ = func() {
+		_ = s1{f: nil}
+	}
+	_ = f
+}