message: Fix build issues with tests
  Caused by incorrect casting with new return types for FileSize and GetFileModificationTime.
diff: @@ -990,13 +990,13 @@ TEST(FileSystemTest,
  TEST(FileSystemTest, WriteFileGetSize) {
  ASSERT_FALSE(FileExists("./test file"));
  EXPECT_TRUE(CreateFile("./test file"));
  - EXPECT_EQ(0, FileSize("./test file"));
  + EXPECT_EQ(0u, FileSize("./test file"));
  unsigned char tmp[] = {'t', 'e', 's', 't'};
  std::vector<unsigned char> data(tmp, tmp + 4);
  EXPECT_TRUE(Write("./test file", data));
  - EXPECT_NE(0, FileSize("./test file"));
  + EXPECT_NE(0u, FileSize("./test file"));
  EXPECT_TRUE(DeleteFile("./test file"));
  EXPECT_FALSE(FileExists("./test file"));
  @@ -1022,13 +1022,14 @@ TEST(FileSystemTest, GetFileModificationTime) {
  EXPECT_TRUE(CreateFile("./test file"));
  - uint64_t modif_time = GetFileModificationTime("./test file");
  - EXPECT_LE(0ul, modif_time);
  + time_t modif_time = GetFileModificationTime("./test file");
  + EXPECT_LE(0ul, static_cast<unsigned long>(modif_time));
  std::vector<uint8_t> data(1, 1);
  EXPECT_TRUE(WriteBinaryFile("./test file", data));
  - EXPECT_LE(0ul, GetFileModificationTime("./test file"));
  + EXPECT_LE(0ul,
  + static_cast<unsigned long>(GetFileModificationTime("./test file")));
  EXPECT_LE(modif_time, GetFileModificationTime("./test file"));
  EXPECT_TRUE(DeleteFile("./test file"));
  