Issue with Visual C++ 2019 Update 4

[JonCavesMSFT]

Hi: We have just made some changes to the Visual C++ compiler that makes the checking of 'extern "C"' functions stricter - especially across namespaces. This has shown up some issues in the file:

https://github.com/leapmotion/autowiring/blob/1c4f51f3db0d87117159698190af5ef6ee6300db/contrib/autoboost/autoboost/date_time/filetime_functions.hpp

Specifically functions like 'GetSystemTimeAsFileTime' which now are flagged as an error as they do not match the declaration in the Windows SDK (because they use a different definition of 'SYSTEMTIME').

Feel free to contact me if you need more information.

Thanks Jonathan Caves