This is a lot of cleanup of memory handling in pkgconf and libpkgconf. With this series all of the unittests are green with the address sanitizer enabled, and the usage in Meson++ and Muon reports no leaks. So, success?
Currently the required_private field gets walked twice, once when the
main required field is walked, and a second time when it is walked
itself. This results in the requires_private field leaking memory.