[ci] Use dated ROOT/llvm tag to build Cling 1.3#827

aaronj0 merged 2 commits intocompiler-research:maincompiler-research/CppInterOp:mainfrom

aaronj0:fix-cling1.3-llvmaaronj0/CppInterOp:fix-cling1.3-llvmCopy head branch name to clipboard