[osx] Fix memory leaks using -fobjc-arc correctly

The -fobjc-arc flags must be specified for the compiler, not in the
linker. This generates a lot of memory leaks when we copy content into
the clipboard (just testing copy/put_image examples with a for loop to
repeat the action can easily show this leak).

This might be the reason of some memory leaks reported on the macOS
port of Aseprite: aseprite/aseprite#4251

CMakeLists.txt

@@ -53,7 +53,7 @@ if(WIN32)
  endif()
  endif()
 elseif(APPLE)
- target_link_options(clip PRIVATE -fobjc-arc)
+ target_compile_options(clip PRIVATE -fobjc-arc)
 
  find_library(COCOA_LIBRARY Cocoa)
  if(COCOA_LIBRARY)