Upstream uses a libcurl more current than Fedora 29.
diff -x '*.orig' -x '*.swp' -x '*.rej' -Naur 10.9-0/FreeFileSync/Source/fs/libcurl/curl_wrap.h 10.9-1/FreeFileSync/Source/fs/libcurl/curl_wrap.h
--- 10.9-0/FreeFileSync/Source/fs/libcurl/curl_wrap.h   2019-02-10 16:42:29.124040824 -0500
+++ 10.9-1/FreeFileSync/Source/fs/libcurl/curl_wrap.h   2019-02-10 20:57:30.758315345 -0500
@@ -75,7 +75,7 @@
             ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UNKNOWN_OPTION);
             ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TELNET_OPTION_SYNTAX);
             ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE50);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE51);
+            //ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE51);
             ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PEER_FAILED_VERIFICATION);
             ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_GOT_NOTHING);
             ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_NOTFOUND);