Do not exclude include directory symlinks to entries of CPATH

Extend the fix from commit 2d0b0e2b9d (Do not exclude include
directories made implicit by CPATH, 2019-05-29, v3.14.5~2^2) to cover
include directories that are symlinks to paths listed in `CPATH`.

Compare resolved paths against resolved entries of `CPATH`.
Resolve the entries as late as possible in case symlinks change.

Fixes: #22383