Fix duplicate definitions in ROOT macros

This pull request affects only unit tests, and only those in packge DataFormats/FWLite.
The unit tests fails in ROOT6 due to duplicate definitions of variables.  In ROOT5, the tests do not fail, because CINT, unlike cling, is not a real compiler, and is permissive of these errors.
This pull request fixes the macros so that each variable is defined only once.