libtoolize must be checked_for and there needs to be a wrapper
that points to GNU libtoolize since that may be installed
as glibtoolize.
This fixes a problem with building Cloog/PPL that was

Reported-by: "Pierrick Brossin" <pierrick@bs-network.net>
Signed-off-by: "Titus von Boxberg" <titus@v9g.de>
(transplanted from c7c9e98d36d8a6a49fcd5f3836d5797bb965eba7)