windows/mpconfigport: Provide off_t definition for MSVC port

For MSVC off_t is defined in sys/types.h but according to the comment earlier in mpconfigport.h this cannot be included directly. So just make off_t the same as mp_off_t. This fixes the build for MSVC with MICROPY_STREAMS_POSIX_API enabled because stream.h uses off_t.

Author: stinos

ports/windows/mpconfigport.h

@@ -232,6 +232,7 @@ typedef __int64 ssize_t;
 #define SSIZE_MAX _I32_MAX
 typedef int ssize_t;
 #endif
+typedef mp_off_t off_t;
 
 
 // Put static/global variables in sections with a known name