The page at
http://www.gnu.org/software/libtool/libtool.html
says that the current stable release of libtool is GNU Libtool 1.4, as
of 26 April 2001.
The Changelog contains several instances of the string "Darwin", in ways
that indicate that maybe it supports building shareable objects on MacOS
X.
Whether it lets you build *run-time loadable* shareable objects is
another matter.
For that matter, I don't know whether the loadable-module support in
GLib will handle Darwin/MacOS X if you build and install GLib with the
latest libtool. I *suspect* that, with all the "it's BSD!" claims,
MacOS X/Darwin might support "dlopen()" and company, but the
configure-script output in the recent mail to one of the Ethereal lists
about MacOS X has
checking for dlfcn.h... no
which suggests that, if it does, it may not do so with the SunOS
4.1[.x]/5.x API that many other UNIXes (commercial and free) have
adopted, so GLib might not support it.
In any case, developers who would build Ethereal release source
tarballs, or who would try to build Ethereal on MacOS X, should probably
consider getting the latest libtool to see whether it results in an
Ethereal that builds more cleanly on MacOS X.