test: add test that gccgo fails to compile

Change-Id: I14d31bb62fd0e26a84f8781644c40918404f5f3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/213899
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

test/fixedbugs/bug507.dir/a.go

@@ -0,0 +1,13 @@
+// Copyright 2020 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 a
+
+type I interface {
+	M()
+}
+
+type S struct {
+	I I
+}

test/fixedbugs/bug507.dir/b.go

@@ -0,0 +1,9 @@
+// Copyright 2020 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 b
+
+import . "./a"
+
+var V2 I

test/fixedbugs/bug507.dir/c.go

@@ -0,0 +1,9 @@
+// Copyright 2020 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 b
+
+import "./a"
+
+var V1 = a.S{I: nil}

test/fixedbugs/bug507.go

@@ -0,0 +1,9 @@
+// compiledir
+
+// Copyright 2020 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 mishandled a combination of normal import and dot import.
+
+package ignored