This feels like a very hacky solution - especially inside a flake.
However, other do the same so I guess it is ok:
https://github.com/edolstra/dwarffs/blob/a536d80ed446d5a442f6c7c9b12c662e48fe60ea/flake.nix#L41

This reverts commit 55c64295.

This doesn't work because callPackage forwards them to the package
without checking whether the package wants them. I guess this is how
it is supposed to work but it doesn't help with my problem then.

This doesn't work:
- simple fixpoint doesn't work with callPackage
- my release.nix won't work either because we cannot pass additional
  overlays to the nixpkgs we get as a flake input

This reverts commit 87e570ce.

crosstool-NG tries to use gcc with prefix and this won't work because it
bypasses the wrapper script.

The custom code returns the overlay instead of all packages but we
can sort-of fake it by filtering the resulting package set.

The custom code doesn't add the new packages to pkgsBuildBuild and it
doesn't create spliced packages for them so it won't work for cross
compiling.

It still doesn't work because the new packages are only added to pkgs
but not pkgs.pkgsBuildBuild etc so callPackage doesn't pass them to the
packages.

Parts of the old buildPhase actually belong in unpack or configure.

- GCC build was failing with warnings/errors for printf. NixOS disables
  hardening for format and pie for gcc so we do the same.
- gdb is built with Python support. The configure check for Python also
  uses -lncurses so we need that as well. The message is rather
  confusing because it claims not to find Python.