Incorrect wheel tag for platform-dependent packages on PyPy

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Debian GNU/Linux 10 (buster)

• Poetry version: 1.0.0

• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/mmaslowskicc/7485e795e3c8fec873515981293fd17c

Issue

When running on PyPy and having the build key in pyproject.toml, Poetry chooses a wheel tags that is not supported by the platform, so it cannot be installed afterwards.

When running docker build . with files from the linked Gist:

Step 6/7 : RUN poetry build
 ---> Running in a893c9f76461
Creating virtualenv wheeltagtest-9TtSrW0h-py3.6 in /root/.cache/pypoetry/virtualenvs
Building wheeltagtest (0.1.0)
 - Building sdist
 - Built wheeltagtest-0.1.0.tar.gz

 - Building wheel
 - Built wheeltagtest-0.1.0-pp369-pypy36_pp73-linux_x86_64.whl
Removing intermediate container a893c9f76461
 ---> c99768df9fda
Step 7/7 : RUN poetry run pip install dist/*.whl
 ---> Running in 33d70ae40527
ERROR: wheeltagtest-0.1.0-pp369-pypy36_pp73-linux_x86_64.whl is not a supported wheel on this platform.
The command '/bin/sh -c poetry run pip install dist/*.whl' returned a non-zero code: 1

A proper wheel tag would contain pp373 instead of pp369: this runs on PyPy 7.3.0 (which is otherwise compatible with Python 3.6.9).

Reproduce the issue with the linked pyproject.toml and Docker setup by running poetry build under PyPy, then installing the generated wheel with poetry run pip install. Trace how the wheel tag is selected. Done means the PyPy 7.3.0 environment receives a compatible pp373 tag and can install the built wheel.