PythonQt: Fix msvc 2010/2012 build issue

See commontk/PythonQt@9c92fd212605b

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Fix "_invalid_parameter_noinfo_noreturn" link error

By ensuring that "undef" of _DEBUG macro is not done before system
includes, it fixes the issue.

This commit is based on what has been within VTK.
See https://github.com/Kitware/VTK/commit/81d4a72c1195437403f1772559c9c28978818f03

See commontk/PythonQt#9

Thanks @Neosettler and @ihnorton for testing the patch.

Reported-by: Neosettler
Merge branch 'pythonqt-9-fix-msvc-2010-2012-build'

* pythonqt-9-fix-msvc-2010-2012-build:
  PythonQt: Fix msvc 2010/2012 build issue