Fix build with µhttpd 0.9.71

The return type of callbacks was changed from int to an enum.

src/journal-remote/journal-gatewayd.c

@@ -349,7 +349,7 @@ static int request_parse_range(
         return 0;
 }
 
-static int request_parse_arguments_iterator(
+static mhd_result request_parse_arguments_iterator(
                 void *cls,
                 enum MHD_ValueKind kind,
                 const char *key,
@@ -796,7 +796,7 @@ static int request_handler_machine(
         return MHD_queue_response(connection, MHD_HTTP_OK, response);
 }
 
-static int request_handler(
+static mhd_result request_handler(
                 void *cls,
                 struct MHD_Connection *connection,
                 const char *url,

src/journal-remote/journal-remote-main.c

@@ -253,7 +253,7 @@ static int process_http_upload(
         return mhd_respond(connection, MHD_HTTP_ACCEPTED, "OK.");
 };
 
-static int request_handler(
+static mhd_result request_handler(
                 void *cls,
                 struct MHD_Connection *connection,
                 const char *url,

src/journal-remote/microhttpd-util.h

@@ -47,6 +47,12 @@
 #  define MHD_create_response_from_fd_at_offset64 MHD_create_response_from_fd_at_offset
 #endif
 
+#if MHD_VERSION >= 0x00097002
+#  define mhd_result enum MHD_Result
+#else
+#  define mhd_result int
+#endif
+
 void microhttpd_logger(void *arg, const char *fmt, va_list ap) _printf_(2, 0);
 
 /* respond_oom() must be usable with return, hence this form. */