sys-apps/texinfo: Add useflag xs (default off) toggling C in Perl
When pure Perl is used, texinfo will be slower, however, there is no need for
rebuilds on Perl upgrade. Since this is our most frequent road bump at the
moment, see portage bug 638914, we take the slowdown by default and hope that
things improve. Not sure how well this will work out, however, since texinfo
again depends on other Perl modules, which are installed in version dependent
paths.
Bug: https://bugs.gentoo.org/638914
Package-Manager: Portage-2.3.67, Repoman-2.3.13
Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>