Automake 1.16.4 included the following change
(https://git.savannah.gnu.org/cgit/automake.git/tree/NEWS):

> The PYTHON_PREFIX and PYTHON_EXEC_PREFIX variables are now set from
> Python's sys.prefix and sys.exec_prefix; use the new configure options
> --with-python_prefix and --with-python_exec_prefix to specify explicitly.

This required some changes to how the our build system expands
autoconf/automake variables to generate the setup.py script for
the wheel build.