Add support for OpenBSD

There were three patches OpenBSD applied to build Irrlicht, and I implemented two of them. The first required turning off joystick events on OpenBSD, and the second (which I didn't confirm was necessary) required some defines in os.h. The third patch would have added an include to CIrrDeviceLinux.cpp, but the file had changed quite a bit and I could not tell whether this was necessary, so I left it out, and it appears Irrlicht builds fine.

include/IrrCompileConfig.h

@@ -142,7 +142,9 @@
 
 
 //! Define _IRR_COMPILE_WITH_JOYSTICK_SUPPORT_ if you want joystick events.
+#if !(defined(__FreeBSD__) || defined(__OpenBSD__))
 #define _IRR_COMPILE_WITH_JOYSTICK_EVENTS_
+#endif
 #ifdef NO_IRR_COMPILE_WITH_JOYSTICK_EVENTS_
 #undef _IRR_COMPILE_WITH_JOYSTICK_EVENTS_
 #endif

source/Irrlicht/os.cpp

@@ -25,11 +25,16 @@
 	#define bswap_16(X) OSReadSwapInt16(&X,0)
 	#define bswap_32(X) OSReadSwapInt32(&X,0)
 	#define bswap_64(X) OSReadSwapInt64(&X,0)
-#elif defined(__FreeBSD__) || defined(__OpenBSD__)
+#elif defined(__FreeBSD__)
 	#include <sys/endian.h>
 	#define bswap_16(X) bswap16(X)
 	#define bswap_32(X) bswap32(X)
 	#define bswap_64(X) bswap64(X)
+#elif defined(__OpenBSD__)
+	#include <endian.h>
+	#define bswap_16(X) letoh16(X)
+	#define bswap_32(X) letoh32(X)
+	#define bswap_64(X) letoh64(X)
 #elif !defined(_IRR_SOLARIS_PLATFORM_) && !defined(__PPC__) && !defined(_IRR_WINDOWS_API_)
 	#include <byteswap.h>
 #else