sem_acquire second argument is not working

### HHVM Version

> Please include the output of `hhvm --version` and `hh_client --version`
HipHop VM 3.30.2 (rel)
Compiler: 1547490784_941975033
Repo schema: f6e390de46500754aba5049064f73b133bcb48fb

hh-c15d5f902880f7478651a85a635cf21d449d0b44-3.30.2 Mon Jan 14 13:35:42 2019

### Operating System and Version
Debian GNU/Linux 8 inside Docker

> For example, 'Debian Squeeze', 'Ubuntu 16.04', 'MacOS High Sierra'. Please
> also mention if you are using Docker or similar images.

### Standalone code, or other way to reproduce the problem
```
$seed='12345678';
$key = \ftok($seed, 'm');
$a = \sem_get($key, 1, 0666, 1);
$s = \sem_acquire($a, true);

if ($s == false) {
echo "Task is already running!";
exit(0);
}
echo 'running....\n';
\sleep(10);
```

> This should not depend on installing any libraries or frameworks. Ideally, it
> should be possible to copy-paste this into a single file and reproduce the
> problem by running `hhvm` and/or `hh_client`

### Actual result

> If applicable, please copy-paste output from `hhvm` or `hh_client`

### Expected result
The second instance of the script must print "Task is already running!" but it waits until the first instance finishes then run the remaining code.