fix compilation with clang-cl

[neheb]

__stdcall is supported by MinGW as well.

[neheb]

hrm so windows headers internally have a

#define WINAPI __stdcall

maybe that should be used instead of __stdcall.

edit: hrm yeah:

#ifndef WINAPI
#if defined(_ARM_)
#define WINAPI
#else
#define WINAPI __stdcall
#endif
#endif

[scheibel]

Thanks for contributing.