The following page on www.g.o mentions that glsa-check is installed with gentoolkit. This is no longer the case. glsa-check is installed with Portage. The reference needs updated. https://www.gentoo.org/support/security/stay-informed.html
gentoolkit is also mentioned providing glsa-check on https://www.gentoo.org/support/security/ as well.
Fixed in the following commit: https://gitweb.gentoo.org/sites/www.git/commit/?id=cef58f3fcbe154efd64f1349ff7f745415dcb3c7