Setting `RUNPATH` to `lib` directory

We vendor some 3rd party dependencies to reduce the number of system deps we have and to ensure consistency between installations.

Whilst evaluating this project as a basis for the python we'd like to ship we noticed that no `RPATH` or `RUNPATH` is set, which prevents loading of shared libraries from the most obvious location being the `lib` directory that is being shipped.

The only ticket I found that seems related is #227

I attempted to set the `RUNPATH` using `pathelf` but for some unknown reason it doesn't have any effect. Setting an `RPATH` worked but since it is deprecated and not really fit for our purpose we would rather not use it.

I'm not sure if it is possible to set a relocatable `RUNPATH` so setting a default one might not be possible. Being able to set one at all would be very useful.

My knowledge in this area is somewhat limited so I might be missing something obvious.

Thoughts?

P.S. the command was `patchelf --set-rpath '/somepath/lib/' /somepath/bin/python3.9` where `somepath` is equivalent to the `python` directory in the release artifacts.