Bug#972762: bornagain doesn't correctly detects python3.9

[Matthias Klose]

Package: src:bornagain
Version: 1.16.0-1
Severity: serious
Tags: sid bullseye
User: debian-python at lists.debian.org
Usertags: python3.9

bornagain ftbfs with python3-defaults from experimental, ending up with a mix of
3.8 and 3.9.

https://people.debian.org/~ginggs/python3.9-default/bornagain_1.16.0-1build1_amd64-2020-10-21T07:22:49Z.build


[...]
-- Found Doxygen: /usr/bin/doxygen (found version "1.8.20") found components:
doxygen missing components: dot
-- Requested Python versions 3.8;3.7;3.6;3.5;3.4;3.3
-- Found PythonInterp: /usr/bin/python3.8 (found version "3.8.6")
-- Found Python interpreter version 3.8.6 at /usr/bin/python3.8
-- Found PythonLibs: /usr/lib/x86_64-linux-gnu/libpython3.9.so (found version
"3.9.0+")
-- Found Python libraries version 3.9.0+ at
/usr/lib/x86_64-linux-gnu/libpython3.9.so; includes at /usr/include/python3.9
-- BORNAGAIN_USE_PYTHON3: ON.
-- --> Validating Python installation corresponding to the interpreter
/usr/bin/python3.8
-- ----> ALT_PYTHON_PREFIX:/usr
-- ----> ALT_PYTHON_INCLUDE_DIRS:/usr/include/python3.8
-- ----> ALT_PYTHON_SITE_PACKAGES:/usr/lib/python3/dist-packages
-- ----> ALT_PYTHON_MODULE_EXTENSION:.cpython-38-x86_64-linux-gnu.so
-- ----> ALT_PYTHON_IS_DEBUG:0
-- ----> ALT_PYTHON_SIZEOF_VOID_P:8
-- ----> ALT_PYTHON_LIBRARY_SUFFIX:3.8
-- ----> Python interpreter reports include directory (see
ALT_PYTHON_INCLUDE_DIRS) which differs from what we have learned before (see
PYTHON_INCLUDE_DIRS).
-- ----> Setting PYTHON_INCLUDE_DIRS=/usr/include/python3.8
-- ---> PYTHON_VERSION_STRING 3.8.6 differs from PYTHONLIBS_VERSION_STRING 3.9.0+
-- ---> There is inconcistency between versions of interpreter and library.
-- --> Python seems to be OK.
[...]