Windows: include direct.h in sys.stat module

On Unicies `sys/stat.h` will provide `mkdir`.  Windows provides the
POSIX requirement through the portable name `_mkdir` which is declared
in the `direct.h` header.  This adds the additional header to the `ucrt`
module to allow access to this function.

Author: compnerd

stdlib/public/Platform/ucrt.modulemap

@@ -95,6 +95,7 @@ module ucrt [system] {
 
         module stat {
           header "sys/stat.h"
+          header "direct.h"
           export *
         }