unix: correct argument order for SyncFileRange syscall on linux/ppc64{,le}

On linux/ppc64{,le} the SYS_SYNC_FILE_RANGE2 syscall is used to
implement SyncFileRange. This syscall has a different argument order
than SYS_SYNC_FILE_RANGE. Apart from that the implementations of both
syscalls are the same, so use a simple wrapper to invoke the syscall
with the correct argument order.

For context see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=edd5cd4a9424f22b0fa08bef5e299d41befd5622

Fixes golang/go#27485

Change-Id: Idc154eab7b7c521a34de821e1d1a97095e96fed0
Reviewed-on: https://go-review.googlesource.com/133215
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_linux_test.go

@@ -7,6 +7,7 @@
 package unix_test
 
 import (
+	"io/ioutil"
 	"os"
 	"runtime"
 	"runtime/debug"
@@ -441,3 +442,26 @@ func TestFaccessat(t *testing.T) {
 		}
 	}
 }
+
+func TestSyncFileRange(t *testing.T) {
+	file, err := ioutil.TempFile("", "TestSyncFileRange")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(file.Name())
+	defer file.Close()
+
+	err = unix.SyncFileRange(int(file.Fd()), 0, 0, 0)
+	if err == unix.ENOSYS || err == unix.EPERM {
+		t.Skip("sync_file_range syscall is not available, skipping test")
+	} else if err != nil {
+		t.Fatalf("SyncFileRange: %v", err)
+	}
+
+	// invalid flags
+	flags := 0xf00
+	err = unix.SyncFileRange(int(file.Fd()), 0, 0, flags)
+	if err != unix.EINVAL {
+		t.Fatalf("SyncFileRange: unexpected error: %v, want EINVAL", err)
+	}
+}