libgo: update to Go1.16beta1 release

This does not yet include support for the //go:embed directive added
in this release.

	* Makefile.am (check-runtime): Don't create check-runtime-dir.
	(mostlyclean-local): Don't remove check-runtime-dir.
	(check-go-tool, check-vet): Copy in go.mod and modules.txt.
	(check-cgo-test, check-carchive-test): Add go.mod file.
	* Makefile.in: Regenerate.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/280172

1 files changed, 12 insertions, 0 deletions

diff --git a/libgo/go/net/net.go b/libgo/go/net/net.go
index 2e61a7c..4b4ed12 100644
--- a/libgo/go/net/net.go
+++ b/libgo/go/net/net.go
@@ -81,6 +81,7 @@ package net
 import (
 	"context"
 	"errors"
+	"internal/poll"
 	"io"
 	"os"
 	"sync"
@@ -632,6 +633,17 @@ func (e *DNSError) Timeout() bool { return e.IsTimeout }
 // error and return a DNSError for which Temporary returns false.
 func (e *DNSError) Temporary() bool { return e.IsTimeout || e.IsTemporary }
 
+// errClosed exists just so that the docs for ErrClosed don't mention
+// the internal package poll.
+var errClosed = poll.ErrNetClosing
+
+// ErrClosed is the error returned by an I/O call on a network
+// connection that has already been closed, or that is closed by
+// another goroutine before the I/O is completed. This may be wrapped
+// in another error, and should normally be tested using
+// errors.Is(err, net.ErrClosed).
+var ErrClosed = errClosed
+
 type writerOnly struct {
 	io.Writer
 }