When checking whether a directory is "implicit" (e.g. implicit link
directory or implicit rpath directory), resolve the real path of both
sides of the comparison.  Otherwise we will not recognize paths like
`/usr/lib32` as implicit when `/usr/lib` is implicit and `lib32` is
actually a symlink to `lib`.  This can lead to addition of unnecessary
entries to the RPATH of a binary, for example.

Fixes: #16682