utils/fs: use <sys/stat.h>, not <sys\stat.h>

Fix cross-compilation failure from linux to windows:
```
  CC utils/unlit/dist-install/build/fs.o
utils/unlit/fs.c:24:10: fatal error: sys\stat.h: No such file or directory
 #include <sys\stat.h>
          ^~~~~~~~~~~~
```

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

utils/fs/fs.c

@@ -21,8 +21,8 @@
 #include <io.h>
 #include <fcntl.h>
 #include <wchar.h>
-#include <sys\stat.h>
-#include <sys\types.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 #include <share.h>
 
 /* This function converts Windows paths between namespaces. More specifically