Draft: add a post-processing step that attempts to make any pkgconfig files reloctable prior to packaging

Code quality is pretty poor, I'll try and improve it when I have the time. :)

There is some prep work done for the ffmpeg tree, it may or may not work (libav* has some special cases handled). Possible pain points: some of these libs look like they may try to link against system libcrypt and liblzma (and possible others), that needs to be redirected to our versions on a by-case basis.

The freetype patch(or a variation) is still required because without it, the paths are not even inside the correct install prefix so this script can't handle them.

Requires ci-utilities!6 (closed)

TODO

• mixing quoted and unquoted unix paths looks like it probably doesnt work
• cleanup