I have to specify '-shrext .so' to let libtool create the dlo's with .so
This should be the default on linux!
Also libtool should say that it needs the package
to compile plugins! The error message is that it can't find /usr/lib/libltdl.la
Oh, I take the .so problem back... it was a packages own 'libtool' ... thought
libtoolize --copy --force would overwrite it.
There's little we can do about fixing broken copies of libtool in upstream
packages, other than talking upstream developers into updating the copy of
libtool they use, and overriding libtool as you've done in the meantime.
As for needing libltdl.la for plugins, what is it that you're trying to do
(command line), and how does it fail (error output)? AFAIK it shouldn't be
necessary to have libltdl.la to create a plugin (as opposed to a program that
uses libltdl), unless you're linking with some other libtool library that was
linked with libltdl itself.
libtool never brings in libltdl by itself, any time it's linked in, it's either
because it was explicitly specified in the command line, or because some other
library you're linking with was linked with it. So it would be this other
library's responsibility to make sure that libltdl.la is available whenever its
own .la file is present.
Not libtools bug, the 'other library' needs to make sure libltdl is installed