Use real path to source dir when checking for roottest and rootbench
Use real path to source dir when checking for roottest and rootbench

Fixes ROOT-8741. The error happens when the source directory is a symlink.

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