test: add test case that failed with gccgo

Updates #26335

Change-Id: Ibfb1e232a0c66fa699842c8908ae5ff0f5d2177d
Reviewed-on: https://go-review.googlesource.com/123316
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue26335.go

+// run
+
+// Copyright 2018 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 passing a struct with an empty field through
+// reflect.Value.Call.
+
+package main
+
+import (
+	"reflect"
+)
+
+type Empty struct {
+	f1, f2 *byte
+	empty struct{}
+}
+
+func F(e Empty, s []string) {
+	if len(s) != 1 || s[0] != "hi" {
+		panic("bad slice")
+	}
+}
+
+func main() {
+	reflect.ValueOf(F).Call([]reflect.Value{
+		reflect.ValueOf(Empty{}),
+		reflect.ValueOf([]string{"hi"}),
+	})
+}