linuxx8664gcc (based on the Opteron's compiler flag __x86_64__). Use this
option when the machine runs in full 64 bit mode under Linux. The Opteron
can also run in full 32 bit compatability mode (use tag linux in that case).


git-svn-id: http://root.cern.ch/svn/root/trunk@6525 27541ba8-7e3a-0410-8455-c3a389f83636