test: add bug426.go: a gccgo crash on valid code

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5715044

test/fixedbugs/bug426.go

+// compile
+
+// Copyright 2012 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.
+
+// gccgo crashed compiling this.
+
+package p
+
+type T *T
+
+func f(t T) {
+	println(t, *t)
+}