Do not call XrdPosixXrootd::setDebug()
It is listed in /usr/include/xrootd/XrdPosix/XrdPosixXrootd.hh after:
// The following methods were always considered private. They are no longer // used and will be removed on the next major release! They are only here for // now to keep ABI compatability for the 4.x and prior releases.
It has been removed in xrootd 5.