curl: Honor OPENSSL_NO_SSL2

Some OpenSSL distributions have dropped support for the ancient SSLv2
protocol completely.  Port changes from upstream curl to recognize this
case and avoid using it.

Utilities/cmcurl/curl/curl.h

@@ -312,7 +312,7 @@ typedef enum {
   CURLE_UNSUPPORTED_PROTOCOL,    /* 1 */
   CURLE_FAILED_INIT,             /* 2 */
   CURLE_URL_MALFORMAT,           /* 3 */
-  CURLE_URL_MALFORMAT_USER,      /* 4 - NOT USED */
+  CURLE_NOT_BUILT_IN,            /* 4 */
   CURLE_COULDNT_RESOLVE_PROXY,   /* 5 */
   CURLE_COULDNT_RESOLVE_HOST,    /* 6 */
   CURLE_COULDNT_CONNECT,         /* 7 */

Utilities/cmcurl/ssluse.c

@@ -1285,8 +1285,13 @@ Curl_ossl_connect_step1(struct connectdata *conn,
     req_method = TLSv1_client_method();
     break;
   case CURL_SSLVERSION_SSLv2:
+#ifdef OPENSSL_NO_SSL2
+    failf(data, "OpenSSL was built without SSLv2 support");
+    return CURLE_NOT_BUILT_IN;
+#else
     req_method = SSLv2_client_method();
     break;
+#endif
   case CURL_SSLVERSION_SSLv3:
     req_method = SSLv3_client_method();
     break;

Utilities/cmcurl/strerror.c

@@ -69,6 +69,10 @@ curl_easy_strerror(CURLcode error)
   case CURLE_URL_MALFORMAT:
     return "URL using bad/illegal format or missing URL";
 
+  case CURLE_NOT_BUILT_IN:
+    return "A requested feature, protocol or option was not found built-in in"
+      " this libcurl due to a build-time decision.";
+
   case CURLE_COULDNT_RESOLVE_PROXY:
     return "couldn't resolve proxy name";
 
@@ -287,7 +291,6 @@ curl_easy_strerror(CURLcode error)
     return "Error in the SSH layer";
 
     /* error codes not used by current libcurl */
-  case CURLE_URL_MALFORMAT_USER:
   case CURLE_FTP_USER_PASSWORD_INCORRECT:
   case CURLE_MALFORMAT_USER:
   case CURLE_BAD_CALLING_ORDER: