add compiler version to INFO output

irc/handlers.go

 	rb.Add(nil, server.name, RPL_INFO, nick, fmt.Sprintf(client.t("This is Oragono version %s."), SemVer))
 	if Commit != "" {
 		rb.Add(nil, server.name, RPL_INFO, nick, fmt.Sprintf(client.t("It was built from git hash %s."), Commit))
+		rb.Add(nil, server.name, RPL_INFO, nick, fmt.Sprintf(client.t("It was compiled using %s."), runtime.Version()))
 	}
 	rb.Add(nil, server.name, RPL_INFO, nick, "")
 	rb.Add(nil, server.name, RPL_INFO, nick, client.t("Oragono is released under the MIT license."))