On Windows in release mode, the test_cext and test_cppext can now
build C and C++ extensions.
* test_cext now also builds the C extension without options.
* test_cppext now also builds the C++ extension without options.
* Add C++14 test to test_cppext; C++11 is not supported by MSVC.
* Make setup_venv_with_pip_setuptools_wheel() quiet when
support.verbose is false. Only show stdout and stderr on failure.
* Move test_cppext to its own directory
* Rename setup_testcppext.py to setup.py
* Rename _testcppext.cpp to extension.cpp
* The source (extension.cpp) is now also copied by the test.
Victor Stinner