Fix: Detect armv8_crc32 programatically for Apple A9

The Apple A9 supports Neon but does not support Arm's crc32 instruction.
This detection does not work on other platforms, however this feature is only used on Apple platforms anyway.

src/fastgltf.cpp

@@ -55,6 +55,9 @@ static_assert(std::string_view { SIMDJSON_TARGET_VERSION } == SIMDJSON_VERSION,
 #elif defined(FASTGLTF_ENABLE_ARMV8_CRC)
 // MSVC does not provide the arm crc32 intrinsics.
 #include <arm_acle.h>
+#ifdef __APPLE__
+#include <sys/sysctl.h>
+#endif
 #endif
 
 namespace fg = fastgltf;
@@ -224,6 +227,11 @@ namespace fastgltf {
 #elif defined(FASTGLTF_ENABLE_ARMV8_CRC)
 		const auto& impls = simdjson::get_available_implementations();
 		if (const auto* neon = impls["arm64"]; neon != nullptr && neon->supported_by_runtime_system()) {
+#ifdef __APPLE__
+			std::int64_t ret = 0;
+			std::size_t size = sizeof(ret);
+			if (sysctlbyname("hw.optional.armv8_crc32", &ret, &size, nullptr, 0) == 0 && ret == 1)
+#endif
 			crcStringFunction = armv8_crc32c;
 		}
 #endif