qt: Add support for Haiku

* OpenAL backend is enabled by default on Haiku
* bswap include now makes use of builtins if they exist
* Use a local fgetws method for Haiku to avoid crashes
* OpenGL renderers are completely disabled on Haiku (they do not work)
* Software renderer is a widget, not a window on Haiku (fixes blank screen)
* Add option to disable System MIDI at compile time

src/network/CMakeLists.txt

@@ -27,3 +27,7 @@ else()
     add_subdirectory(slirp)
     target_link_libraries(86Box slirp)
 endif()
+
+if (HAIKU)
+    target_link_libraries(86Box network)
+endif()