Is there a reason to define FRONTEND for TBase?

[yazun]

pg_config --cppflags
-DFRONTEND -D_GNU_SOURCE -I/usr/include/libxml2

It quite counterintuitive and It causes headaches with some extensions, see tada/pljava#347 (comment)

I could imagine intra-node protocol part is dependent on it, but maybe there's a cleaner way?