tools/yuvcmp: add HAVE_UNISTD_H around #include <unistd.h>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tools/yuvcmp.c

@@ -9,8 +9,10 @@
 #include <stdio.h>
 #include <sys/stat.h>
 #include <fcntl.h>
-#include <unistd.h>
 
+#if HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 
 int
 main(int argc, char **argv)