libmpdec has always been a separate project, predating the integration
into Python-3.3.  Before the Python-3.3 release, Jim Jewett suggested
a cleaner library/module separation (and he was right, it made the
code much more readable).

Then distributors wanted --with-system-libmpdec, so here we are.


Let's discuss the _decimal capsule API in #15237.


As for the libmpdec symbols: I agree it is somewhat unclean to
do this on the Python side.

For *some* functions it is also tricky (but by no means impossible)
to use them directly and expect the same results as from _decimal.

Maybe a solution for numba is to just assume --with-system-libmpdec.
libmpdec is extremely easy to package, distributions just have to
ensure that their Python version matches the libmpdec version.