Summary:
Similar to[[ https://phabricator.kde.org/D1216 |  D1216 ]] add procctl call to disable ptrace on FreeBSD.

We cannot do the procfs-lookup to check whether the process is already being run inside gdb -- however, on FreeBSD, we could use the P_TRACED flag of the process to figure this out:
> sys/proc.h:#define P_TRACED        0x00800 /* Debugged process being traced. */

And the code would look something similar to

```
    pid_t pid = getpid();
    struct procstat *prstat = procstat_open_sysctl();
    struct kinfo_proc *procinfo;
    unsigned int cnt;
    procinfo = procstat_getprocs(prstat, KERN_PROC_PID, pid, &cnt);
    long p_flags = procinfo->ki_flag;
    int p_traced = p_flags & P_TRACED;
    if (p_traced != P_TRACED) {
        mode = PROC_TRACE_CTL_DISABLE;
        procctl(P_PID, getpid(), PROC_TRACE_CTL, &mode);
    }
    procstat_freeprocs(prstat,procinfo);
    procstat_close(prstat);
```

But as wayland is [far] in the future on FreeBSD, and that check above is a bit lengthy, I think it is enough if we add it once it is needed.

Reviewers: rakuco, graesslin

Reviewed By: graesslin

Subscribers: plasma-devel

Projects: #plasma

Differential Revision: https://phabricator.kde.org/D1425