sysconfig-debian-schemes.diff patch causes Python packages to FTBFS

[Jeremy Bícha]

This weekend, we noticed that link-grammar fails to build from source because of a change in python3.6. I've now found a second case with redshift.

These packages still build in Debian unstable. Therefore, it looks like the sysconfig-debian-schemes patch is to blame.

The "fix" for link-grammar looks wrong. It does not feel like it would be an improvement to update all affected packages like this.

It's interesting that autopkgtest did its job here by link-grammar failing its tests but the failure was basically quickly ignored.

References
==========
https://launchpad.net/ubuntu/+source/python3.6/3.6.5-9ubuntu1

https://autopkgtest.ubuntu.com/packages/l/link-grammar/cosmic/amd64
https://launchpad.net/ubuntu/+source/link-grammar/5.5.0-1ubuntu1

https://launchpad.net/ubuntu/+source/redshift/1.11-2ubuntu1/+build/14876053

https://irclogs.ubuntu.com/2018/05/12/%23ubuntu-devel.html

[Dmitry Shachnev (mitya57)]

This also affects pybind11 and xtensor-python autopkgtests, because Python reports wrong include path:

$ python3.6 -c "import sysconfig; print(sysconfig.get_path('platinclude'))"
/usr/local/include/python3.6m

On Debian it prints the correct path:

$ python3.6 -c "import sysconfig; print(sysconfig.get_path('platinclude'))"
/usr/include/python3.6m

The build system uses the following code to get Python include path:

https://github.com/pybind/pybind11/blob/e763f046899ce09bf8a586ea75a7d9a9d27e70e4/tools/FindPythonLibsNew.cmake#L76

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dmitry Shachnev (mitya57)]

In the latest python3.6 sync, sysconfig-debian-schemes.diff is disabled, so I think we can consider this bug fixed.

[Matthias Klose (doko)]

this is reverted for now