Description:
------------
Calling shmop_open() with a $key that matches IPC_PRIVATE (which
is usually zero on POSIX, and always zero on Windows), creates
private shared memory on POSIX, but not on Windows.

This is actually not particularly related to ext/shmop, but rather
to our Windows emulation layer for XSI shared memory (shmget() and
friends), so all extensions which use that functionality to create
private SHM are affected by this.  For instance, APCu[1].

[1] <https://github.com/krakjoe/apcu/issues/394>


Test script:
---------------
<?php
$write = 'test';

$shm1 = shmop_open(0, 'c', 0777, 1024);
shmop_write($shm1, $write, 0);

$shm2 = shmop_open(0, 'c', 0777, 1024);
$read = shmop_read($shm2, 0, 4);

var_dump(is_string($read) && $read !== $write);

shmop_close($shm1);
shmop_close($shm2);
?>


Expected result:
----------------
bool(true)

Actual result:
--------------
bool(false)