pkg/53560: devel/py-pluggy does not build for PYTHON_VERSION>27

[triaxx%NetBSD.org@localhost]

>Number:         53560
>Category:       pkg
>Synopsis:       devel/py-pluggy does not build for PYTHON_VERSION>27
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Aug 28 12:40:00 +0000 2018
>Originator:     Frédéric Fauberteau
>Release:        netbsd-8-0-RELEASE (pkgsrc-2018Q2)
>Organization:
>Environment:
NetBSD hydralisk 8.0 NetBSD 8.0 (HYDRALISK) #2: Thu Aug 23 13:57:31 CEST 2018  root@hydralisk:/usr/obj/sys/arch/amd64/compile/HYDRALISK amd64
>Description:
py-pluggy build fails with the following log:
~~~~~~~~~~
===> Building for py36-pluggy-0.7.1
(cd [...] python3.6  setup.py  build  -j3)
Download error on https://pypi.org/simple/setuptools-scm/: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:841) -- Some packages may not be found!
Couldn't find index page for 'setuptools-scm' (maybe misspelled?)
Download error on https://pypi.org/simple/: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:841) -- Some packages may not be found!
No local packages or working download links found for setuptools-scm
Traceback (most recent call last):
  File "setup.py", line 43, in <module>
    main()
  File "setup.py", line 38, in main
    packages=['pluggy'],
  File "/home/triaxx/pkg/lib/python3.6/site-packages/setuptools/__init__.py", line 139, in setup
    _install_setup_requires(attrs)
  File "/home/triaxx/pkg/lib/python3.6/site-packages/setuptools/__init__.py", line 134, in _install_setup_requires
    dist.fetch_build_eggs(dist.setup_requires)
  File "/home/triaxx/pkg/lib/python3.6/site-packages/setuptools/dist.py", line 514, in fetch_build_eggs
    replace_conflicting=True,
  File "/home/triaxx/pkg/lib/python3.6/site-packages/pkg_resources/__init__.py", line 777, in resolve
    replace_conflicting=replace_conflicting
  File "/home/triaxx/pkg/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1060, in best_match
    return self.obtain(req, installer)
  File "/home/triaxx/pkg/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1072, in obtain
    return installer(requirement)
  File "/home/triaxx/pkg/lib/python3.6/site-packages/setuptools/dist.py", line 581, in fetch_build_egg
    return cmd.easy_install(req)
  File "/home/triaxx/pkg/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 670, in easy_install
    raise DistutilsError(msg)
distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('setuptools-scm')
*** Error code 1
~~~~~~~~~~

But py27-pluggy-0.7.1 builds successfully.
>How-To-Repeat:
Set PYTHON_VERSION_DEFAULT to 34, 35, 36 or 37
cd devel/py-pluggy && make install
>Fix:
Install devel/py-setuptools_scm fixes the build but I am not convinced by this workaround and I have the feeling that it should be in lang/python/egg.mk...