eiskaltdcpp-2.2.11-25.20190922gita85c5d8.fc33 fails to build in Fedora 33:

[ 83%] Linking CXX executable eiskaltdcpp-gtk
cd /home/test/fedora/eiskaltdcpp/eiskaltdcpp-eiskaltdcpp-a85c5d8/eiskaltdcpp-gtk && /usr/bin/cmake -E cmake_link_script CMakeFiles/eiskaltdcpp-gtk.dir/link.txt --verbose=1
/usr/bin/c++  -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -std=c++14 -pipe -Wformat -Werror=format-security -fPIC -D_FORTIFY_SOURCE=2 -O2 -g -DNDEBUG  -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -Wl,--as-needed -rdynamic CMakeFiles/eiskaltdcpp-gtk.dir/src/UserCommandMenu.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/WulforUtil.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/adlsearch.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/bacon-message-connection.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/bookentry.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/cmddebug.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/dialogentry.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/downloadqueue.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/emoticons.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/emoticonsdialog.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/entry.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/favoritehubs.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/favoriteusers.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/finishedtransfers.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/hashdialog.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/hub.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/mainwindow.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/notify.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/previewmenu.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/privatemessage.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/publichubs.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/search.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/searchspy.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/settingsdialog.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/settingsmanager.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/sharebrowser.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/sound.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/transfers.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/treeview.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/uploadqueue.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/wulfor.cc.o CMakeFiles/eiskaltdcpp-gtk.dir/src/wulformanager.cc.o  -o eiskaltdcpp-gtk  -Wl,-rpath,/home/test/fedora/eiskaltdcpp/eiskaltdcpp-eiskaltdcpp-a85c5d8/dcpp: -lX11 -lXext -lfreetype -lglib-2.0 -lgobject-2.0 -lgdk_pixbuf-2.0 -lgdk-3 -lgtk-3 -lcairo -lpango-1.0 -latk-1.0 -lboost_system -lc -lnotify -lgthread-2.0 -llua -lm ../dcpp/libeiskaltdcpp.so.2.4 ../dht/libdht.a -lpthread -lbz2 -lz -lssl -lcrypto -llua -lm ../extra/libextra.a -lminiupnpc -lc -lpcrecpp -lpcre -lidn -lattr -lboost_system
/usr/bin/ld: CMakeFiles/eiskaltdcpp-gtk.dir/src/WulforUtil.cc.o:/home/test/fedora/eiskaltdcpp/eiskaltdcpp-eiskaltdcpp-a85c5d8/eiskaltdcpp-gtk/src/WulforUtil.hh:28: multiple definition of `isEmptyString'; CMakeFiles/eiskaltdcpp-gtk.dir/src/UserCommandMenu.cc.o:/home/test/fedora/eiskaltdcpp/eiskaltdcpp-eiskaltdcpp-a85c5d8/eiskaltdcpp-gtk/src/WulforUtil.hh:28: first defined here

A difference between a passing and failing build root is at <https://koschei.fedoraproject.org/build/8247628>.