draw: Do not use LLVM's opaque types.

draw: Do not use LLVM's opaque types.

Contrary what the name may suggest, LLVM's opaque types are used for
recursive types -- types whose definition refers itself -- so opaque
types correspond to pre-declaring a structure in C. E.g.:

   struct node;

   struct link {
      ....
      struct node *next;
   };

   struct node {
      struct link link;
   }

Void pointers are also disallowed by LLVM. So the suggested way of creating
what's commonly referred as "opaque pointers" is using byte pointer (i.e.,
uint8_t * ).