Systemd has had a single -dev binary package since ~2014, so these have
not worked for a long time.

Noted in systemd#138 (but not the main thrust of the issue)

There is no great solution. Python.h expects to be included first and to be
allowed to pollute the define namespace. We don't want to do that, because in
other places we want to include sd-messages.h early, and also we want to use a
higher standard than the obsolete version that Python.h declares.
Unfortunately, there is no nice solution to this problem. So call #undef
enough times to silence warnings and after including the header, define the
standard for our code to a recent version.

It seems some gcc versions enable it by default, so we get a lot
of warnings.

Silence warnings

This might now work because pypi changes its rules, but at
least update to modern names of the commands for now.

This helps to get it installed.

Clean up Makefile and add license file declaration