os: File.Sync should return *PathError on Plan 9

[fhs]

File.Sync currently returns *SyscallError on Plan 9. It should return *PathError so that the error type matches other systems.

What version of Go are you using (go version)?

$ go version
go version devel +master Sat Jun 20 01:48:54 EDT 2020 plan9/amd64

What did you do?

Run:

package main

import (
	"fmt"
	"os"
)

func main() {
	err := os.Stderr.Sync()
	if err != nil {
		fmt.Printf("%T: %v\n", err, err)
	}
}

What did you expect to see?

Filename in the error, for example on Linux:

*os.PathError: sync /dev/stderr: invalid argument

What did you see instead?

*os.SyscallError: fsync: permission denied

@gopherbot add labels OS-Plan9, NeedsFix

[ianlancetaylor]

CC @0intro

[gopherbot]

Change https://golang.org/cl/239857 mentions this issue: os: return *PathError error in File.Sync on Plan 9