move tarball generation to tox.ini

and change the Makefile to delegate the "tarballs" target to tox

This should fix the ticket:2910 problem of the "tarballs" buildbot failing.

Makefile

@@ -218,9 +218,8 @@ test-pip-install:
 
 # TARBALL GENERATION
 .PHONY: tarballs
-tarballs:
-	$(MAKE) make-version
-	$(PYTHON) setup.py sdist --formats=bztar,gztar,zip bdist_wheel
+tarballs: # delegated to tox, so setup.py can update setuptools if needed
+	tox -e tarballs
 
 .PHONY: upload-tarballs
 upload-tarballs:

tox.ini

@@ -120,3 +120,9 @@ deps =
 # See https://pyinstaller.readthedocs.io/en/stable/advanced-topics.html#creating-a-reproducible-build
 setenv=PYTHONHASHSEED=1
 commands=pyinstaller -y --clean pyinstaller.spec
+
+[testenv:tarballs]
+deps =
+commands =
+         python setup.py update_version
+         python setup.py sdist --formats=bztar,gztar,zip bdist_wheel