Haiku support

This adds support for building SIMH on Haiku, with pthread, dlopen, SDL.
No pcap support yet.

For the record, the haikuports recipe is at:
http://bb.haikuports.org/haikuports/src/7911743b56a3/app-emulation/simh/

Btw, you might want to remove the CRLF on some files,
as it broke automatic patching with haikuporter.
cf. https://help.github.com/articles/dealing-with-line-endings

You might also want to clean up the nested ifeq in the makefile, it doesn't make it easy to merge things.
The ifdefs could probably be simplified as well...