Windows builds with setup.py fail about gsd HOT 1 CLOSED

Working with @joaander, we identified the problem. The gsd file was being opened in "text mode" because the _O_BINARY flag wasn't being defined. This was the result of preprocessor directives: CMake sets WIN32, but the setup.py installation doesn't set that. Instead, we should rely on _WIN32, which is set by the compiler instead of the build environment.

Temporarily, we enabled these flags in setup.py to help with debugging on Windows:

fl = Extension('gsd.fl',
               sources=['gsd/fl.c', 'gsd/gsd.c'],
               include_dirs = [numpy.get_include()],
               extra_compile_args=['/Z7', '/Od'],
               extra_link_args=['/DEBUG']
               )

References:
https://cmake.org/cmake/help/latest/variable/WIN32.html
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/open-wopen?view=vs-2019
https://docs.microsoft.com/en-us/cpp/c-runtime-library/text-and-binary-mode-file-i-o?view=vs-2019

from gsd.