Although libtool is optimised to not need to subconfigure libltdl,

Although libtool is optimised to not need to subconfigure libltdl,
the installed libltdl sources for libtoolize need to put
libltdl/configure.ac in the parent package so that *it* can
subconfigure libltdl.  That way we don't put any constraints on
the build system used by the parent package because the
libtoolized libltdl subtree is a self-contained sub-project:

* libltdl/Makefile.am (EXTRA_DIST): Add configure.ac.
(nobase_ltdldata_DATA): Change back to libltdl's own
configure.ac.