pgsql: Replace use of deprecated Python module distutils.sysconfig, tak

Replace use of deprecated Python module distutils.sysconfig, take 2.

With Python 3.10, configure spits out warnings about the module
distutils.sysconfig being deprecated and scheduled for removal in
Python 3.12. Change the uses in configure to use the module sysconfig
instead. The logic stays largely the same, although we have to
rely on INCLUDEPY instead of the deprecated get_python_inc function.

Note that sysconfig exists since Python 2.7, so this moves the minimum
required version up from Python 2.6. Also, sysconfig didn't exist in
Python 3.1, so the minimum 3.x version is now 3.2.

We should consider back-patching this if it gives no further trouble,
as the no-longer-supported versions are old enough to probably not
be interesting to anyone.

Peter Eisentraut, Tom Lane, Andres Freund

Discussion: https://postgr.es/m/c74add3c-09c4-a9dd-1a03-a846e5b2fc52@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bd233bdd8dd95ea127a921998847724c44295736

Modified Files
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config/python.m4 | 33 +++++++++++++--------------------
configure | 37 +++++++++++++++----------------------
doc/src/sgml/installation.sgml | 6 +++---
3 files changed, 31 insertions(+), 45 deletions(-)