start-hyprland: *BSD needs non-prctl() implementation

[jg1uaa]

prctl() (defined at <sys/prctl.h>) is Linux-only.
FreeBSD has procctl() (<sys/procctl.h>) but other *BSDs not.

If start-hyprland is mandatory to launch hyprland, non-prctl() code is required.

[vaxerski]

MRs welcome