Bug #15327: configure: --with-tcp-port option being partially ignored

make sure that if builder configured with a non-standard (!= 3306)
default TCP port that value actually gets used throughout. if they
didn't configure a value, assume "use a sensible default", which
will be read from /etc/services or, failing that, from the factory
default. That makes the order of preference
- command-line option
- my.cnf, where applicable
- $MYSQL_TCP_PORT environment variable
- /etc/services (unless configured --with-tcp-port)
- default port (--with-tcp-port=... or factory default)

tests/mysql_client_test.c

@@ -15759,7 +15759,13 @@ static struct my_option client_test_long_options[] =
   {"password", 'p',
    "Password to use when connecting to server. If password is not given it's asked from the tty.",
    0, 0, 0, GET_STR, OPT_ARG, 0, 0, 0, 0, 0, 0},
-  {"port", 'P', "Port number to use for connection", (char **) &opt_port,
+  {"port", 'P', "Port number to use for connection or 0 for default to, in "
+   "order of preference, my.cnf, $MYSQL_TCP_PORT, "
+#if MYSQL_PORT_DEFAULT == 0
+   "/etc/services, "
+#endif
+   "built-in default (" STRINGIFY_ARG(MYSQL_PORT) ").",
+   (char **) &opt_port,
    (char **) &opt_port, 0, GET_UINT, REQUIRED_ARG, 0, 0, 0, 0, 0, 0},
   {"server-arg", 'A', "Send embedded server this as a parameter.",
    0, 0, 0, GET_STR, REQUIRED_ARG, 0, 0, 0, 0, 0, 0},