LArSoft

Data products in LArSoft used to hide part of the code from ROOT 5 by enclosing it in #ifndef __GCCXML__ guards. This was necessary due to the... limitations of CINT and friends.
ROOT 6 is using rootcling instead, whose level of understanding is basically the same as gcc. Those guards are therefore not needed. But, more to the point, rootcling does not define __GCCXML__ any more, so those guards are ineffective and misleading.
LArSoft should consider removing them or replacing them with __ROOTCLING__ guards, which are the equivalent in the new world.

To be more explicit: that they are not needed is proven by the fact that they have been ignored since LArSoft 6.0.1, and nobody has reported any related problem since.