include unistd.h if present to prevent compiler warnings on close()

lib/memdebug.c

@@ -58,6 +58,10 @@
 #include <string.h>
 #include <stdlib.h>
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 /* DONT include memdebug.h here! */
 
 /*