this is necessary for manylinux toolchains where there's no
linkable libpython

Adding this macro in your source tree with a list of module names
will give you a 'dependent_bindings' target to build and if you don't
set ```-DDXT_NO_AUTO_BINDINGS_DEPENDS=TRUE``` this is added as a
dependency for the local 'bindings' target

This adds the state of https://github.com/pybind/pybind11.git, #f4eec655.