[cmake] IS_DIRECTORY "works best" with full paths:
[cmake] IS_DIRECTORY "works best" with full paths:

Fixes ROOT_GENERATE_DICTIONARY not finding v7 headers.

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