Don't hide C++11 constructs from ROOT 6

In CMSSW header files exposed to CINT in ROOT 5, C++11 constructs are must be hidden from CINT, Usually with preprocessor symbols (e.g __GCCXML__, _MAKECINT__).  In ROOT 6, this hiding is not
necessary.  Unfortunately, there is no consistency in the symbols used.  Some are defined in ROOT 6,
some are not.
I have discovered one case, in TrackingRecHits.h, where the current use of such a preprocessor symbol
causes a run time JIT compilation error in ROOT6.  This is because this class contains a data member
that is a std::shared_ptr, but due to conditional compilation, the JIT compiler sees it as a bare pointer.
This leads to a JIT compilation error because, while std::shared_ptr<T>::element is defined, "element"
is not defined for a bare pointer.  Th fix is to use a preprocessor symbol, __GCCXML__ that is defined only for ROOT 5, so that the JIT compilation sees the shared_ptr.  For consistency. this change is made in two closely related packages.
This pull request is a no-op for ROOT 5, and is being requested for code commonality between the 7_2_X branch and the 7_2_ROOT6_X branch.