Fix rustc 1.42.0.
@@ -6,6 +6,7 @@ use crate::syntax::{
};
use quote::{format_ident, quote};
use std::collections::HashSet;
+use std::u32;
use syn::punctuated::Punctuated;
use syn::{
Abi, Error, Expr, ExprLit, Fields, FnArg, ForeignItem, ForeignItemFn, ForeignItemType,
