add create directory api for iOS and macOS

src/asset.cpp

@@ -4,6 +4,7 @@
 
 #ifdef __APPLE__
 #include <Foundation/Foundation.h>
+#include "objc_utils.h"
 #endif
 
 #ifdef __ANDROID__
@@ -141,6 +142,8 @@ bool Asset::create_dir(const std::string& path)
     return PathFileExistsA(path.c_str()) ? true : CreateDirectoryA(path.c_str(), NULL);
 #elif __ANDROID__
     return android_create_dir(path);
+#elif __IOS__ || __OSX__
+    return apple_create_dir(path);
 #endif
 }