Add missing includes
pair_hash.h uses std::size_t and std::hash but does not include the
corresponding headers <cstddef> and <functional>.
Change-Id: I194a5c76e8f50b1574e1359f616351581033c576
diff --git a/internal/ceres/pair_hash.h b/internal/ceres/pair_hash.h
index 1e7ddeb..83ff2b4 100644
--- a/internal/ceres/pair_hash.h
+++ b/internal/ceres/pair_hash.h
@@ -1,5 +1,5 @@
// Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2018 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
// http://ceres-solver.org/
//
// Redistribution and use in source and binary forms, with or without
@@ -33,7 +33,9 @@
#ifndef CERES_INTERNAL_PAIR_HASH_H_
#define CERES_INTERNAL_PAIR_HASH_H_
+#include <cstddef>
#include <cstdint>
+#include <functional>
#include <utility>
#include "ceres/internal/export.h"
