add missing include of ../config.h in regress/*.c

otherwise we get a nice 'no previous prototype' due to
-Wmissing-prototypes.

compat/getdtablesize.c

@@ -14,6 +14,8 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "../config.h"
+
 #include <unistd.h>
 
 int

compat/memmem.c

@@ -23,6 +23,8 @@
  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
+#include "../config.h"
+
 #include <string.h>
 #include <stdint.h>
 

compat/setresgid.c

@@ -14,6 +14,8 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "../config.h"
+
 #include <sys/types.h>
 #include <unistd.h>
 

compat/setresuid.c

@@ -14,6 +14,8 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "../config.h"
+
 #include <sys/types.h>
 
 #include <errno.h>