build.py script in source code overrides 'build' tool

[blazewicz (Krzysztof Błażewicz)]

I found this issue while investigating ​https://trac.macports.org/ticket/64425.

When source code of Python project contains a script called build.py or a submodule called build it will override global installation of the build tool. This is when MacPorts invokes /path/to/python -m build ... local script/module will be invoked instead of intended tool. In such cases pep517 build will always fail.

Issue begun after ​https://github.com/macports/macports-ports/commit/e94c8a1 and so far I found that it affects py-pendulum port.