internal/poll: only export FD.eofError for testing on posix systems

Fixes build on plan9.

Change-Id: Idbb1e6887c24a873de77c92095198847ed953278
Reviewed-on: https://go-review.googlesource.com/36915
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/internal/poll/export_posix_test.go

+// Copyright 2017 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+
+// Export guts for testing on posix.
+// Since testing imports os and os imports internal/poll,
+// the internal/poll tests can not be in package poll.
+
+package poll
+
+func (fd *FD) EOFError(n int, err error) error {
+	return fd.eofError(n, err)
+}

src/internal/poll/export_test.go

@@ -33,7 +33,3 @@ func (mu *FDMutex) RWLock(read bool) bool {
 func (mu *FDMutex) RWUnlock(read bool) bool {
 	return mu.rwunlock(read)
 }
-
-func (fd *FD) EOFError(n int, err error) error {
-	return fd.eofError(n, err)
-}