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/include/86box/plat.h

@@ -40,7 +40,7 @@ extern int stricmp(const char* s1, const char* s2);
 extern int strnicmp(const char* s1, const char* s2, size_t n);
 #endif
 
-#if (defined(__unix__) || defined(__APPLE__)) && !defined(__linux__)
+#if (defined(__HAIKU__) || defined(__unix__) || defined(__APPLE__)) && !defined(__linux__)
 /* FreeBSD has largefile by default. */
 # define fopen64        fopen
 # define fseeko64       fseeko