regent: Support LLVM 11 in setup_env.py.
regent: Support LLVM 11 in setup_env.py.

StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion