setup.py: report modules which built but import failed (closes #21282)

Patch by Lukas Vacek.
Issue #10650: Remove the non-standard 'watchexp' parameter from the
Decimal.quantize() method in the Python version.  It had never been
present in the C version.
Issue #19962: The Windows build process now creates "python.bat"
in the root of the source tree, which passes all arguments through
to the most recently built interpreter.
Unite 'Build' sections of Misc/NEWS