Fix string.h, strings.h and stdio.h include in crypto backend.

String.h and stdbool.h are already included in main backend header,
no need to include them again.

Stdio.h is missing for OpenSSL and NSS backed (for sprintf).

Strings.h is missing for cipher_generic, gcrypt and OpoenSSL (strcasecmp).

Fixes: #885

lib/crypto_backend/cipher_generic.c

@@ -19,9 +19,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <string.h>
-#include <stdbool.h>
 #include <errno.h>
+#include <strings.h>
 #include "crypto_backend.h"
 
 struct cipher_alg {

lib/crypto_backend/crc32.c

@@ -38,8 +38,6 @@
  *
  */
 
-#include <stdio.h>
-
 #include "crypto_backend.h"
 
 static const uint32_t crc32_tab[] = {

lib/crypto_backend/crypto_cipher_kernel.c

@@ -19,10 +19,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <string.h>
 #include <stdlib.h>
 #include <stdio.h>
-#include <stdbool.h>
 #include <errno.h>
 #include <unistd.h>
 #include <sys/socket.h>

lib/crypto_backend/crypto_gcrypt.c

@@ -19,9 +19,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <string.h>
 #include <stdio.h>
 #include <errno.h>
+#include <strings.h>
 #include <gcrypt.h>
 #include <pthread.h>
 #include "crypto_backend_internal.h"

lib/crypto_backend/crypto_kernel.c

@@ -19,7 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <string.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <errno.h>

lib/crypto_backend/crypto_nettle.c

@@ -20,7 +20,6 @@
  */
 
 #include <stdlib.h>
-#include <string.h>
 #include <errno.h>
 #include <nettle/sha.h>
 #include <nettle/sha3.h>

lib/crypto_backend/crypto_nss.c

@@ -19,7 +19,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <string.h>
+#include <stdio.h>
 #include <errno.h>
 #include <nss.h>
 #include <pk11pub.h>

lib/crypto_backend/crypto_openssl.c

@@ -28,9 +28,10 @@
  * for all of the code used other than OpenSSL.
  */
 
-#include <string.h>
+#include <stdio.h>
 #include <errno.h>
 #include <limits.h>
+#include <strings.h>
 #include <openssl/crypto.h>
 #include <openssl/evp.h>
 #include <openssl/hmac.h>