xdt-autogen: You must have "libtoolize" installed
Running xdt-autogen from xfce4-dev-tools 4.17.0 (in the libxfce4-util 4.16.0 source directory but I don't think that's relevant) on macOS 10.15.7 produces this error:
xdt-autogen: You must have "libtoolize" installed. You can get if from
https://www.gnu.org/software/libtool/.
Apple includes a script in macOS called "libtool" which is completely unrelated to GNU libtool. For this reason, on macOS, GNU libtool is seldom installed as libtool and libtoolize but rather as glibtool and glibtoolize.
Code to find and use glibtoolize used to be present in xdt-autogen in xfce4-dev-tools 4.16.0 but it was removed in 2759f19c thereby causing this problem.