default-gcc-version: Remove conditional for vc4 and relibc

[Artturin]

gcc6 was removed in a42d18b

relibc was removed in e6f33f4

pkgsCross.vc4.stdenv.cc is broken in the patching of binutils

Description of changes

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[emilazy]

LGTM; thanks! But this is being bumped to 14 in #340612, so maybe this should go to staging instead to avoid a merge conflict?

I wonder if this conditional in pkgs/development/compilers/gcc/common/dependencies.nix might be dubious for the same reason:

  ++ optionals (with stdenv.targetPlatform; isVc4 || isRedox && flex != null) [ flex ]

[Artturin]

Will rebase.

Vc4 support hasn't been completely ripped out yet so let's not remove other conditionals

CC @cleverca22 who uses it in https://github.com/librerpi/lk-overlay/blob/f2a7f7497f36e0a05cfdd3c930305566c50771c2/default.nix#L29

[emilazy]

Vc4 support hasn't been completely ripped out yet so let's not remove other conditionals

Right; was just wondering if it was somehow a proxy for a GCC 6‐specific thing considering the otherwise‐unlikely pairing of VC4 and Redox.