This adds the required changes/checks so that the build can run on
FreeBSD.
There are a few things that differ between FreeBSD and Linux:
- CPU probes return -1 for CPU usage
- `hot_threads` cannot be supported on FreeBSD
From OpenJDK's `os_bsd.cpp`:
```c++
bool os::is_thread_cpu_time_supported() {
#ifdef __APPLE__
return true;
#else
return false;
#endif
}
```
So this API now returns (for each FreeBSD node):
```
curl -s localhost:9200/_nodes/hot_threads
::: {Devil Hunter Gabriel}{q8OJnKCcQS6EB9fygU4R4g}{127.0.0.1}{127.0.0.1:9300}
hot_threads is not supported on FreeBSD
```
- multicast fails in native `join` method - known bug:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=193246
Which causes:
```
1> Caused by: java.net.SocketException: Invalid argument
1> at java.net.PlainDatagramSocketImpl.join(Native Method)
1> at java.net.AbstractPlainDatagramSocketImpl.join(AbstractPlainDatagramSocketImpl.java:179)
1> at java.net.MulticastSocket.joinGroup(MulticastSocket.java:323)
1> at org.elasticsearch.plugin.discovery.multicast.MulticastChannel$Plain.buildMulticastSocket(MulticastChannel.java:309)
```
So these tests are skipped on FreeBSD.
Resolves#15562
482843e27b