* Move it into separate win32_snprintf.h file to de-duplicate its
implementation from all miniupnp source files.
* Do not use this emulation with mingw32 SDK when __NO_ISOCEXT is not
defined as in this case mingw32 provides working snprintf function.
* Fix detection for mingw-w64 variants, when __NO_ISOCEXT is defined or
when older version without UCRT is used.
* Add check if _scprintf function is available. In case it is not available
just returns length of filled buffer to prevent buffer overflow.
Pali Rohár