net: don't fail test if splice fails because pipe2 is missing

This reportedly happens on CentOS 5.11.  The real code will work fine;
    this test is assuming that the unexported slice function will handle
    the splice, but if pipe2 does not work then it doesn't.  The relevant
    code in internal/poll/splice_linux.go says "Falling back to pipe is
    possible, but prior to 2.6.29 splice returns -EAGAIN instead of 0 when
    the connection is closed."
    
    Reviewed-on: https://go-review.googlesource.com/138838

From-SVN: r264793

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-53d0d7ca278a5612fcdb5fb098e7bf950a0178ef
+098e36f4ddfcf50aeb34509b5f25b86d7050749c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/net/splice_test.go

@@ -11,7 +11,9 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"os"
 	"sync"
+	"syscall"
 	"testing"
 )
 
@@ -225,6 +227,10 @@ func testSpliceReaderAtEOF(t *testing.T) {
 	serverUp.Close()
 	_, err, handled := splice(serverDown.(*TCPConn).fd, serverUp)
 	if !handled {
+		if serr, ok := err.(*os.SyscallError); ok && serr.Syscall == "pipe2" && serr.Err == syscall.ENOSYS {
+			t.Skip("pipe2 not supported")
+		}
+
 		t.Errorf("closed connection: got err = %v, handled = %t, want handled = true", err, handled)
 	}
 	lr := &io.LimitedReader{