[core] Expand envvars in TCling::AddIncludePath (ROOT-9062).
[core] Expand envvars in TCling::AddIncludePath (ROOT-9062).

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