Added include protection for unistd.h and sys/time.h.

diff --git a/dlls/dsound/mixer.c b/dlls/dsound/mixer.c
index cdc3034..c6e7013 100644
--- a/dlls/dsound/mixer.c
+++ b/dlls/dsound/mixer.c
@@ -24,7 +24,9 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/fcntl.h>
-#include <unistd.h>
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
 #include <stdlib.h>
 #include <string.h>
 #include <math.h>	/* Insomnia - pow() function */