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/pitch_sse4_1.c

@@ -29,6 +29,8 @@
 #include "config.h"
 #endif
 
+#if defined (__i386__) || defined(__x86_64__)
+
 #include <xmmintrin.h>
 #include <emmintrin.h>
 
@@ -193,3 +195,4 @@ void xcorr_kernel_sse4_1(const opus_val16 * x, const opus_val16 * y, opus_val32
     _mm_storeu_si128((__m128i *)sum, initSum);
 }
 #endif
+#endif