Consider symlinks when checking implicit directories

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 (closed)