The tkinter module is part of the Python's standard library, however it is in
a separate subpackage to save an unwanted dependency on tk.
When tk is installed, we recommend the subpackage to provide more upstream-like
experience, but still provide a way out.
The bcond flatpackage assumed that if building *without* flatpackage,
that we want to build the main Python for the distribution. However, in
some instances we want a non-flatpackage build of Python that is *not*
the main Python in the distro.
Therefore I have split the main-Python setting into its own bcond.
