Add BSD Unix build support (FreeBSD, OpenBSD, NetBSD, ..).
Add BSD Unix build support (FreeBSD, OpenBSD, NetBSD, ..).

* Builds fine on FreeBSD.
* OpenBSD returns build errors on `build_ext()` call.

Signed-off-by: Tomasz 'CeDeROM' CEDRO <ea73344294b1c6e2cb529d7fc98a4971de7607ac@cedro.info>

kivy/pyjnius,kivy/pyjnius,kivy/pyjnius