net: add hurd build tag for setReadMsgCloseOnExec

Patch from Svante Signell.

	PR go/103573
	PR go/104290

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/386216

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-3742e8a154bfec805054b4ebf0809f12dc7694da
+90ed127ef053b758288af9c4e43473e257770bc3
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/net/unixsock_readmsg_cloexec.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build aix || darwin || freebsd || solaris
+//go:build aix || darwin || freebsd || hurd || solaris
 
 package net