make dist after make maintainer-clean no XS for pod2texi

Hello,

I just did a commit to set TEXINFO_XS=omit for the pod2texi calls, such
that they succeed even if the XS modules are not built already:

https://cgit.git.savannah.gnu.org/cgit/texinfo.git/commit/?id=514b6b209e66ef1c1a6c90dd8ecbcca1388286ab

Previously, the XS modules not loading would have lead to a silent use
of pure Perl modules.  Now it errors out since the changes in march.  In
a way this is a good thing, as an objective of the change was to always
be certain of the state with respect to XS vs pure Perl.

I am not sure that the current situation is the best, though, as now
pod2texi will always use the pure Perl modules.

Any remark, idea?

-- 
Pat