[rootcling] We do not need to filter the build system junk.
[rootcling] We do not need to filter the build system junk.

Since root-project/root@10a0dec we do not expose flags from the build system
directly to rootcling. We use that opportunity to simplify the setup while
preparing rootcling for the new argument parser.

karies/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,olifre/root,karies/root,karies/root,olifre/root,karies/root,olifre/root,karies/root,olifre/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,karies/root