Fix fuzzy.dll functions on Win32 prebuilt binary

[a4lg]

On fuzzy.dll (in the prebuilt Win32 archive), fuzzy_hash_file and fuzzy_hash_stream functions will not work properly if you normally build the program which uses fuzzy.dll with Visual C++.

Cause

Because struct FILE is managed by separate instance of Microsoft CRT, mixing multiple CRTs (multiple versions or Debug/Release builds) causes problems. Internally, POSIX file descriptor is managed by __pioinfo and its entry (struct __crt_lowio_handle_data on UCRT) has corresponding Win32 handle and other information. Since every instance of Microsoft CRT has its own __pioinfo (note: on universal CRT [VS2015 or later], __pioinfo is no longer exported), mixing CRT can cause serious inconsistency problems:

• File opened by fopen is not considered open.
• Different file is referenced.

Potential Errors Passing CRT Objects Across DLL Boundaries: https://msdn.microsoft.com/en-us/library/ms235460.aspx

Possible Resolution

fuzzy.dll references msvcrt.dll and there's no problem if Win32 program also uses msvcrt.dll. However, this is very unlikely. Programs built on Visual C++ are normally linked against version-specific CRT and/or universal CRT.

Although it's possible to link against version-specific CRT (but not universal CRT; as of September 2017), it's much safer to build fuzzy.dll on Visual C++. At least, linking against universal CRT (new CRT for Windows; ucrtbase.dll and API sets) is required to resolve this issue because there will be no version-related issues anymore (there will be however, Debug/Release DLL issues).

• Fix README for CRT object sharing (adding /MD or /MDd option; will be committed later)
• Make fuzzy.c, edit_distn.c and find-file-size.c possible to compile on Visual C++
• Make build pipeline to use “platform toolset” feature on Visual C++
• Build fuzzy.dll with multiple platform toolsets (Debug build and Release build):
  • Visual Studio 2015 (v140) (mandatory; linked against universal CRT)
  • Visual Studio 2013 (v120) (optional)
  • Visual Studio 2012 (v110) (optional)

After these changes, Windows build pipeline may be separated from this repository.