Fix warnings that appeared after enabling link-time optimizations

client.c

@@ -23,15 +23,15 @@ bool http_client_do( const void** opt )
 	for(;;){
 		switch( (long int)*opt ) {
 			case 1: // HTTP_REQ_URL
-				curl_easy_setopt(curl, CURLOPT_URL, opt[1] );
+				curl_easy_setopt(curl, CURLOPT_URL, (const char*)opt[1] );
 				opt += 2;
 				break;
 			case 2: // HTTP_REQ_HEADER
-				headers = curl_slist_append(headers, opt[1] );
+				headers = curl_slist_append(headers, (const char*)opt[1] );
 				opt += 2;
 				break;
 			case 3: // HTTP_REQ_OUTFILE
-				curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writer);
+				curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, (curl_write_callback)writer);
 				curl_easy_setopt(curl, CURLOPT_WRITEDATA, opt[1] );
 				opt += 2;
 				break;