This patch adds a UTC helper `llvm/utils/update_llubi_test_checks.py` to
generate check lines for the trace. Generalizer and multiple prefixes
are not supported since they are meaningless for traces. I know it is a
bit weird, but I don't have a better idea :(
I found that `llvm/utils/update_test_body.py` also works. But it is
annoying to duplicate the command twice.