add missing config.h headers in C files

src/common/acl.c

@@ -14,6 +14,7 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <config.h>
 #include <string.h>
 #include <stdlib.h>
 #include <assert.h>

src/common/hex.c

@@ -14,6 +14,7 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <config.h>
 #include <ctype.h>
 #include <stdint.h>
 #include <stdlib.h>

src/utils/nsec3hash/nsec3hash_main.c

@@ -14,6 +14,7 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <config.h>
 #include <assert.h>
 #include <stdbool.h>
 #include <stdint.h>