Please add an updated version to portage tree.
I cannot find version 7.1.1 at https://gcc.gnu.org/releases.html The latest version there is 7.1, released on 2017-05-02
https://gcc.gnu.org/develop.html#num_scheme X.Y.1 is not any release, but version reported by snapshots built from development branch. Next release after 7.1.0 will be 7.2.0.