Support ARM64 builds on macOS

Author: DataTriny

bindings/c/accesskit.cmake

@@ -3,6 +3,9 @@ set(_accesskit_toolchain "")
 
 if (APPLE)
     set(_accesskit_os "macos")
+    if (CMAKE_OSX_ARCHITECTURES MATCHES "(ARM64|arm64|aarch64)")
+        set(_accesskit_arch "arm64")
+    endif()
 elseif (UNIX)
     set(_accesskit_os "linux")
 elseif (WIN32)