the inode numbers of files.
This should fix the "duplicated macros" error when aclocal is
invoked with `-I ${X11BASE}/share/aclocal' explicitly.
- Do not scan ${X11BASE}/share/aclocal if it does not exist. (Or it's
(a symlink to)* a directory)
This should fix the "no such directory" error when you build a non-X
port without X installed. (like on bento)