Upgrades to Xcode project and Apple Silicon support

- Reorganized Xcode project
- Added missionpack support to Xcode project
- Incorporated changes from MaddTheSane for Apple Silicon support https://github.com/maddthesane/ioq3
- Built SDL 2.0.14 for Apple Siicon, added to existing SDL dylib
- Built SDLMain for Apple Silicon, added to existing libSDL2main.a

code/opus-1.2.1/silk/x86/VAD_sse.c

@@ -29,6 +29,8 @@
 #include "config.h"
 #endif
 
+#if defined (__i386__) || defined(__x86_64__)
+
 #include <xmmintrin.h>
 #include <emmintrin.h>
 #include <smmintrin.h>
@@ -275,3 +277,4 @@ opus_int silk_VAD_GetSA_Q8_sse4_1(                  /* O    Return value, 0 if s
     RESTORE_STACK;
     return( ret );
 }
+#endif