runtime/fcntl

[leongross]

Rework of #4481

[aykevl]

This is not quite correct. If you look at where runtime.fcntl is used, the code looks like this:

func Fcntl(fd int, cmd int, arg int) (int, error) {
        val, errno := fcntl(int32(fd), int32(cmd), int32(arg))
        if val == -1 {
                return int(val), syscall.Errno(errno)
        }
        return int(val), nil
}

So val needs to be -1 when there's an error.
This probably means you can simplify the code like this:

Suggested change

	ret = int32(libc_fcntl(int(fd), int(cmd), int(arg)))
	if ret < 0 {
	return 0, int32(*libc_errno_location())
	}
	return ret, 0
	ret = int32(libc_fcntl(int(fd), int(cmd), int(arg)))
	errno = *libc_errno_location()
	return