speech-dispatcher-git: ltdl library missing

[Rob]

When trying to install speech-dispatcher from git, I got the following error:
./configure -q --prefix=/usr --sysconfdir=/etc --localstatedir=/var --disable-static
configure: error: in `/tmp/s/speechd':
configure: error: ltdl library missing
See `config.log' for more details
My googling showed that ltdl is part of libtool, which is already installed. The host is Debian 9.
Any thoughts here?