FFI: Add ffi.gc() function for finalization of cdata objects.

src/lj_ctype.c

@@ -540,7 +540,7 @@ GCstr *lj_ctype_repr_complex(lua_State *L, void *sp, CTSize size)
 /* -- C type state -------------------------------------------------------- */
 
 /* Initialize C type table and state. */
-void lj_ctype_init(lua_State *L)
+CTState *lj_ctype_init(lua_State *L)
 {
   CTState *cts = lj_mem_newt(L, sizeof(CTState), CTState);
   CType *ct = lj_mem_newvec(L, CTTYPETAB_MIN, CType);
@@ -568,6 +568,7 @@ void lj_ctype_init(lua_State *L)
     }
   }
   setmref(G(L)->ctype_state, cts);
+  return cts;
 }
 
 /* Free C type table and state. */