runtime, syscall: add a couple of hurd build tags

Patch by Svante Signell.

Updates PR go/93468

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/216959

gcc/go/gofrontend/MERGE

-5b438257e6fe5f344ae2f973313f394cda85bf62
+d796680b5a78f686ed118578e81d5b1adf48508d
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/nbpipe_pipe2.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.
 
-// +build freebsd linux netbsd openbsd solaris
+// +build freebsd hurd linux netbsd openbsd solaris
 
 package runtime
 

libgo/go/syscall/sockcmsg_unix_other.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.
 
-// +build aix darwin freebsd linux netbsd openbsd solaris
+// +build aix darwin freebsd hurd linux netbsd openbsd solaris
 
 package syscall