test: new test for issue 31637

This pair of packages caused a crash in gollvm, due to a glitch in the
way the front end handles empty/non-name parameters for functions that
are inline candidates.

Updates #31637.

Change-Id: I571c0658a00974dd36025e571638c0c836a3cdfd
Reviewed-on: https://go-review.googlesource.com/c/go/+/173617
Run-TryBot: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

test/fixedbugs/issue31637.dir/a.go

+// Copyright 2019 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 dO struct {
+	x int
+}
+
+type EDO struct{}
+
+func (EDO) Apply(*dO) {}
+
+var X EDO

test/fixedbugs/issue31637.dir/b.go

+// Copyright 2019 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 main
+
+import "./a"
+
+type No struct {
+	a.EDO
+}
+
+func X() No {
+	return No{}
+}
+
+func main() {
+	X()
+}

test/fixedbugs/issue31637.go

+// compiledir
+
+// Copyright 2019 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.
+
+// This directory contains a pair of packages that triggered
+// a compiler crash in gollvm (problem in handling an inlinable
+// method with unnamed parameter). See issue 31637 for details.
+
+package ignored