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/celt/x86/vq_sse2.c

@@ -30,6 +30,8 @@
 #include "config.h"
 #endif
 
+#if defined (__i386__) || defined(__x86_64__)
+
 #include <xmmintrin.h>
 #include <emmintrin.h>
 #include "celt_lpc.h"
@@ -215,3 +217,4 @@ opus_val16 op_pvq_search_sse2(celt_norm *_X, int *iy, int K, int N, int arch)
 }
 
 #endif
+#endif