enhance RPATH wrappers to avoid duplicate/useless entries

[boegel]

The list of paths that get included in the RPATH section is currently quite long, and we're seeing signs of trouble that may be related to this (see for example easybuilders/easybuild-easyconfigs#11909).

We should:

• avoid including duplicate paths, including paths that are symlinks to an already included path (like lib64 -> lib)
• avoid including paths that don't container any (library) files (somewhat related to directories that don't contain any library files shouldn't be added to $LD_LIBRARY_PATH #3504)

[boegel]

Partially fixed in #3538 (w.r.t. duplicate paths & symlinked paths)

[boegel]

The patchelf tool has an option to shrink the RPATH section to just what's needed to find the required libraries: patchelf --shrink-rpath