fix Xcode mysterious build error

Core/MMKV_OSX.cpp

@@ -91,7 +91,7 @@ void MMKV::minimalInit(MMKVPath_t defaultRootDir) {
     // crc32 instruction requires A10 chip, aka iPhone 7 or iPad 6th generation
     int device = 0, version = 0;
     GetAppleMachineInfo(device, version);
-#    ifdef __aarch64__
+#    ifdef MMKV_USE_ARMV8_CRC32
     if ((device == iPhone && version >= 9) || (device == iPad && version >= 7)) {
         CRC32 = mmkv::armv8_crc32;
     }

Core/crc32/Checksum.h

@@ -18,7 +18,8 @@
  * limitations under the License.
  */
 
-#pragma once
+#ifndef CHECKSUM_H
+#define CHECKSUM_H
 #ifdef __cplusplus
 
 #include "../MMKVPredef.h"
@@ -39,6 +40,8 @@ uLong crc32(uLong crc, const Bytef *buf, z_size_t len);
 
 #    ifdef __aarch64__
 
+#        define MMKV_USE_ARMV8_CRC32
+
 namespace mmkv {
 uint32_t armv8_crc32(uint32_t crc, const uint8_t *buf, size_t len);
 }
@@ -57,4 +60,5 @@ extern CRC32_Func_t CRC32;
 
 #endif // MMKV_EMBED_ZLIB
 
-#endif
+#endif // __cplusplus
+#endif // CHECKSUM_H

Core/crc32/crc32_armv8.cpp

@@ -20,7 +20,7 @@
 
 #include "Checksum.h"
 
-#ifdef __aarch64__
+#ifdef MMKV_USE_ARMV8_CRC32
 
 #    include <zlib.h>
 
@@ -110,4 +110,4 @@ TARGET_ARM_CRC uint32_t armv8_crc32(uint32_t crc, const uint8_t *buf, size_t len
 
 } // namespace mmkv
 
-#endif // __aarch64__
+#endif // MMKV_USE_ARMV8_CRC32