Fix build error on Mac and Linux

Author: yhirose

httplib.h

@@ -2198,6 +2198,10 @@ make_basic_authentication_header(const std::string &username,
 
 namespace detail {
 
+bool is_file(const std::string &path);
+
+bool is_dir(const std::string &path);
+
 std::string encode_query_param(const std::string &value);
 
 std::string decode_url(const std::string &s, bool convert_plus_to_space);
@@ -2525,16 +2529,6 @@ inline std::string base64_encode(const std::string &in) {
   return out;
 }
 
-inline bool is_file(const std::string &path) {
-  struct stat st;
-  return stat(path.c_str(), &st) >= 0 && S_ISREG(st.st_mode);
-}
-
-inline bool is_dir(const std::string &path) {
-  struct stat st;
-  return stat(path.c_str(), &st) >= 0 && S_ISDIR(st.st_mode);
-}
-
 inline bool is_valid_path(const std::string &path) {
   size_t level = 0;
   size_t i = 0;
@@ -2577,6 +2571,16 @@ inline bool is_valid_path(const std::string &path) {
   return true;
 }
 
+inline bool is_file(const std::string &path) {
+  struct stat st;
+  return stat(path.c_str(), &st) >= 0 && S_ISREG(st.st_mode);
+}
+
+inline bool is_dir(const std::string &path) {
+  struct stat st;
+  return stat(path.c_str(), &st) >= 0 && S_ISDIR(st.st_mode);
+}
+
 inline std::string encode_query_param(const std::string &value) {
   std::ostringstream escaped;
   escaped.fill('0');

test/test.cc

@@ -7563,8 +7563,8 @@ TEST(UniversalClientImplTest, Ipv6LiteralAddress) {
 }
 
 TEST(FileSystemTest, FileAndDirExistenceCheck) {
-  std::string file_path = "./www/dir/index.html";
-  std::string dir_path = "./www/dir";
+  auto file_path = "./www/dir/index.html";
+  auto dir_path = "./www/dir";
 
   EXPECT_TRUE(detail::is_file(file_path));
   EXPECT_FALSE(detail::is_dir(file_path));