Fix enum bitfields passed to stdarg functions

VT_ENUM types use the .ref member and can be VT_BITFIELD,
so we need to copy it as well.  Simply do it always.

tccgen.c

@@ -4058,6 +4058,7 @@ static void gfunc_param_typed(Sym *func, Sym *arg)
             gen_cast(&type);
         } else if (vtop->type.t & VT_BITFIELD) {
             type.t = vtop->type.t & (VT_BTYPE | VT_UNSIGNED);
+	    type.ref = vtop->type.ref;
             gen_cast(&type);
         }
     } else if (arg == NULL) {