My build still fails though, now on linking:
/home/src1/src/sailfish/syncevolution/src/syncevo/GLibSupport.h:991:77: error: 'signon_auth_session_process_async' was not declared in this scope
new SYNCEVO_GLIB_CALL_ASYNC_CXX(_prepare)::CXXFunctionCB_t(_cb))
But I don't particularly care anymore, as accumulator has made a version available on OpenRepos!