[dictgen] Make options only required if inside rootcling
[dictgen] Make options only required if inside rootcling

Otherwise they will interfere with LLVM's option parsing.

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root