wnaspi32: Protect the inclusion of dirent.h in aspi.c.

This allows the file to be compiled on platforms that don't have the
header file, such as MSVC.

dlls/wnaspi32/aspi.c

diff --git a/dlls/wnaspi32/aspi.c b/dlls/wnaspi32/aspi.c
index 196b968..c511524 100644
--- a/dlls/wnaspi32/aspi.c
+++ b/dlls/wnaspi32/aspi.c
@@ -40,7 +40,9 @@
 #include <sys/ioctl.h>
 #endif
 #include <fcntl.h>
-#include <dirent.h>
+#ifdef HAVE_DIRENT_H
+# include <dirent.h>
+#endif
 #ifdef HAVE_UNISTD_H
 # include <unistd.h>
 #endif