+BOOL inline imagelist_has_alpha( HIMAGELIST himl, UINT index )
+{
+    return himl->has_alpha && himl->has_alpha[index];
+}

This should be a static function. If you really need it for other files later,
you should add it to the comctl32 private header instead of the public header
commctrl.h. You can also remove inline as compilers should automatically decide
it for you.

Thanks,
Zhiyi