* cmake: Add Haiku as a supported platform
* move mixer.cc to platform-specific as Haiku doesn't use OSS
* Add haiku.h with some stubs
* Use haiku.h
* Add some Haiku stubs
* Some Haiku network workarounds
It does not define SUN_LEN, provide a default.
It doesn't name the union in struct ifreq, use ifr_addr directly.
It seems Linux also declares it so it should work without change.
We can always define it for other platforms lacking it (add a cmake test ?).
Haiku does not have IFF_RUNNING, IFF_LINK seems close in semantics, so use it.
* Haiku: Minimal implementation of update_meminfo & get_top_info
* Haiku: implement update_cpu_usage
