windows/msvc: Fix warnings regarding function declarations.

Fix missing mkdir and gettimeofday declarations, then silence msvc-specific
compiler warning C4996: 'The POSIX name for this item is deprecated'.

ports/unix/modos.c

@@ -33,6 +33,9 @@
 #include <stdlib.h>
 #include <string.h>
 #include <dirent.h>
+#ifdef _MSC_VER
+#include <direct.h> // For mkdir
+#endif
 #include "py/mpconfig.h"
 
 #include "py/runtime.h"