Abstract out on-demand loading of FFI library.

src/lj_bcread.c

@@ -399,11 +399,7 @@ static int bcread_header(LexState *ls)
   if ((flags & BCDUMP_F_FFI)) {
 #if LJ_HASFFI
     lua_State *L = ls->L;
-    if (!ctype_ctsG(G(L))) {
-      ptrdiff_t oldtop = savestack(L, L->top);
-      luaopen_ffi(L);  /* Load FFI library on-demand. */
-      L->top = restorestack(L, oldtop);
-    }
+    ctype_loadffi(L);
 #else
     return 0;
 #endif