Add definition for LCG build of gcc 11.2
LCG dev3 and dev4 moved to gcc 11.2, so we need this definition to be able to build our corresponding slots.
Note that we also need to have gcc/11.2.0-8a51a and binutils/2.37-355ed deployed in /cvmfs/lhcb.cern.ch/lib/lcg/releases