package/avahi: fix build without C++

Commit 02bd5eb59ff113203ea60ffee68bfdbacc4c9245 wrongly removed
avahi_cv_sys_cxx_works=yes as a result, build fails without C++

Fixes:
 - http://autobuild.buildroot.org/results/3d3596ad386144609549693c0a1aa9b704ba748c

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
1 file changed