When using the multiple outputs setup hooks, is it possible to define per-output propagated dependencies besides manually adding them to the relevant file in the nix-support directory of the output?

As an example, a header-only output may have a dependency on another derivation’s header-only output. My understanding is that the current way to handle this would be to add the dependency in propagatedBuildInputs, though that would add the dependency to every output, correct?

In reply to @truby:matrix.org
I wanted to test something from gcc's git master branch, is it difficult to get a stdenv with a gcc built from there? I tried the obvious (overriding gcc-unwrapped's src = ..) and it doesn't build, it seems to still be trying to apply patches even though I have patches = [];
Am I missing something to get this working, or is it just more difficult than this?

vcunat: do you remember what needed --oldincludedir= in https://github.com/NixOS/nixpkgs/commit/def75f028240ce2d38ec8e0707cc886c8b7596a4#diff-d5ce1dbe37e35a5baa932aac914a2f1a32ac46267f9400f2fff393f31d4aa44bR36 ? Looking at https://www.gnu.org/prep/standards/html_node/Directory-Variables.html it feels like it's something that predates gcc. It now breaks sqlite-3.49.0 https://github.com/NixOS/nixpkgs/pull/373944#issuecomment-2645813426

And I wonder if we should just drop --oldincludedir= completely.