build: Fix Sysprof interface path with split sysprof package
When sysprof-4 and libsysprof-capture-4 are installed into different prefixes, such as with Nix package manager, the D-Bus interfaces are likely not discoverable from the latter package.
(Nixpkgs started passing the new -Dinstall-static=false
option to the main sysprof package as part of GNOME 43 updates.)
cc @chergert