Use HAVE_STRING_H and HAVE_STDLIB_H.

src/server/cache-database.c

@@ -9,8 +9,12 @@
 
 #include <stdio.h>
 #include <stdarg.h>
-#include <string.h>
-#include <stdlib.h>
+#ifdef HAVE_STRING_H
+#  include <string.h>
+#endif
+#ifdef HAVE_STDLIB_H
+#  include <stdlib.h>
+#endif
 #include <time.h>
 #include "cache-database.h"
 #include "smalloc.h"