building the GNU C++ standard library separately from GCC inspired by https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/gcc/libgcc/default.nix.

Main motivation is #132340

Have compiled some simple programs against it, and it seems to be working, but it might be broken in subtle ways I am missing. Also, it might be broken regards to cross compiling.

If we were to merge this, it would probably be a good idea to delete pkgs/development/libraries/gcc/libstdc++/5.nix, since that derivation is much more specific, and doesn't seem to be in use anywhere else in nixpkgs.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 22.11 Release Notes (or backporting 22.05 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
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.