wincng: Cleaned up includes and check NTSTATUS using macro

Removed header file combination that is not supported on a real
Windows platform and can only be compiled using MinGW. Replaced
custom NTSTATUS return code checks with BCRYPT_SUCCESS macro.
wincng: Added cast for double to unsigned long conversion
wincng: Fixed use of possible uninitialized variable pPaddingInfo

Reported by Bob Kast, thanks a lot.
openssl: Check for LIBSSH2_OPENSSL in order to compile with openssl
wincng: fix cross-compilation against the w64 mingw-runtime package