again

% clang++ $(root-config --cflags) hsimple.C $(root-config --libs) $(root-config --ldflags)
Undefined symbols for architecture arm64:
  "_main", referenced from:
      <initial-undefines>
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)