From parrot-3.6.0/config/auto/opengl.pm: # opengl depends on thunks which depend on pcre return $self->_handle_no_opengl($conf) unless $conf->data->get('HAS_PCRE'); So the configuration USE="opengl,-pcre" is invalid (and interpreted as USE="-opengl,-pcre"). I suggest you switch the ebuild to EAPI=4 and add REQUIRED_USE="opengl? ( pcre )".
+ 27 Dec 2011; Patrick Lauer <patrick@gentoo.org> +parrot-3.11.0-r1.ebuild, + -parrot-3.11.0.ebuild: + REQUIRED_USE fix for #377389, eapi4