"Unused private field" build failure(s) — clang 4.0.1

clang -Wall -Werror will fail because bar is private (by default) and never used. g++ does not complain here.
class foo
{
    int bar;
};
PackageVersionSupposed error messageFull log Bug report
clementine 1.3.1+git276-g3485bbe43+dfsg-1playlistundocommands.h:112:7: error: private field 'column_' is not used [-Werror,-Wunused-private-field] Log
drbd-utils 8.9.10-2./CompactDisplay.h:159:19: error: private field 'out' is not used [-Werror,-Wunused-private-field] Log
lmms 1.1.3-7AutomatableModel.h:310:8: error: private field 'm_oldValue' is not used [-Werror,-Wunused-private-field] Log
openni2 2.2.0.33+dfsg-8DDK/XnPixelStream.h:135:9: error: private field 'm_bAllowCustomResolutions' is not used [-Werror,-Wunused-private-field] Log

4 errors