If one or more bashrc files exist in the following locations, they will be sourced before the ebuild is executed in the following order:
/etc/portage/bashrc
/etc/portage/env/${CATEGORY}/${PN}
/etc/portage/env/${CATEGORY}/${PN}:${SLOT}
/etc/portage/env/${CATEGORY}/${P}
/etc/portage/env/${CATEGORY}/${PF}