Piotr Caban (@piotr) commented about include/msvcrt/stdlib.h:
_ACRTIMP size_t __cdecl _mbstrlen(const char*); _ACRTIMP _onexit_t __cdecl _onexit(_onexit_t); _ACRTIMP int __cdecl _putenv(const char*); +_ACRTIMP int __cdecl _putenv_s(const char*,const char*);
Please change return type to errno_t (please also change it in implementation).