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/sound/midi_rtmidi.cpp

@@ -13,12 +13,15 @@
  *          Copyright 2021 Cacodemon345.
  *          Copyright 2021 Miran Grca.
  */
-#if defined __has_include
-#  if __has_include (<RtMidi.h>)
-#    include <RtMidi.h>
-#  endif
-#  if __has_include (<rtmidi/RtMidi.h>)
-#    include <rtmidi/RtMidi.h>
+
+#ifdef SYSTEM_MIDI
+#  if defined __has_include
+#    if __has_include (<RtMidi.h>)
+#      include <RtMidi.h>
+#    endif
+#    if __has_include (<rtmidi/RtMidi.h>)
+#      include <rtmidi/RtMidi.h>
+#    endif
 #  endif
 #endif
 
@@ -35,9 +38,10 @@ extern "C"
 #include <86box/midi_rtmidi.h>
 #include <86box/config.h>
 
-
+#ifdef SYSTEM_MIDI
 static RtMidiOut *    midiout = nullptr;
 static RtMidiIn *    midiin = nullptr;
+#endif
 static int        midi_out_id = 0, midi_in_id = 0;
 static const int    midi_lengths[8] = {3, 3, 3, 3, 2, 2, 3, 1};
 
@@ -49,6 +53,7 @@ rtmidi_write(uint8_t val)
 }
 
 
+#ifdef SYSTEM_MIDI
 void
 rtmidi_play_msg(uint8_t *msg)
 {
@@ -231,6 +236,76 @@ rtmidi_in_get_dev_name(int num, char *s)
 {
     strcpy(s, midiin->getPortName(num).c_str());
 }
+#else /* !SYSTEM_MIDI */
+void
+rtmidi_play_msg(uint8_t *msg)
+{
+
+}
+
+
+void
+rtmidi_play_sysex(uint8_t *sysex, unsigned int len)
+{
+
+}
+
+
+void*
+rtmidi_init(const device_t *info)
+{
+	return nullptr;
+}
+
+
+void
+rtmidi_close(void *p)
+{
+
+}
+
+
+int
+rtmidi_get_num_devs(void)
+{
+	return 0;
+}
+
+
+void
+rtmidi_get_dev_name(int num, char *s)
+{
+
+}
+
+
+void*
+rtmidi_input_init(const device_t *info)
+{
+	return nullptr;
+}
+
+
+void
+rtmidi_input_close(void* p)
+{
+
+}
+
+
+int
+rtmidi_in_get_num_devs(void)
+{
+	return 0;
+}
+
+
+void
+rtmidi_in_get_dev_name(int num, char *s)
+{
+
+}
+#endif
 
 static const device_config_t system_midi_config[] =
 {