not sure which one exactly as I could not find anything on the neon page (admitedly i did not look extensively ..), but with 2.6.0 i get compiler errors about undefined variables/#defines .. 2.8.5 compiles
Please attach build log and config.log.
will have a look asap
ChangeLog of net-misc/neon-0.29.1 says that this version fixes building with GnuTLS < 2.8.0, so I'm closing this bug.