This was proposed by abbradar in #150801, but left out of the follow up PR
#221851 by Ma27 to reduce the size of the diff. Compared to the initial
proposal this includes the callPackage call in the recursion, which avoids
breaking the withJIT/withoutJIT helpers.
In terms of nixpkgs, this is a pure refactor, no derivations change. However,
this makes downstream expressions like the following possible:
(postgresql.override { jitSupport = true; }).pkgs.postgis
This would have not worked before without passing another "this" argument,
which is error prone as can be seen in this example:
https://github.com/PostgREST/postgrest/pull/3222/files
4b6bce5c31