tools: Enable warnings for more binaries/libs

tools: Enable warnings for more binaries/libs

Because WARN_CFLAGS and COVERAGE_CFLAGS are not set globally, we
rely on each binary built to include WARN_CFLAGS/COVERAGE_CFLAGS.
But it is easy to forget those - e.g. libvirt_shell.la. However,
don't enable WARN_FLAGS (i.e. don't include AM_CFLAGS) for
wireshark plugin - parts of that code are generated and trigger
some warnings.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>