include: Fix build on platforms without ECC.

include/libssh/libcrypto.h

@@ -40,6 +40,8 @@ typedef MD5_CTX*  MD5CTX;
 typedef HMAC_CTX* HMACCTX;
 #ifdef HAVE_ECC
 typedef EVP_MD_CTX *EVPCTX;
+#else
+typedef void *EVPCTX;
 #endif
 
 #define SHA_DIGEST_LEN SHA_DIGEST_LENGTH