cudaPackages: fix cudaGencode when cudaForwardCompat is true (closes #215436)

[ConnorBaker]

Description of changes

Closes #215436.

Before:

nix-repl> legacyPackages.x86_64-linux.cudaPackages_11_8.cudaFlags.cudaGencode
[ "-gencode=arch=compute_35,code=sm_35" "-gencode=arch=compute_50,code=sm_50" "-gencode=arch=compute_52,code=sm_52" "-gencode=arch=compute_60,code=sm_60" "-gencode=arch=compute_61,code=sm_61" "-gencode=arch=compute_70,code=sm_70" "-gencode=arch=compute_75,code=sm_75" "-gencode=arch=compute_80,code=sm_80" "-gencode=arch=compute_86,code=sm_86" "-gencode=arch=compute_compute_86,code=compute_compute_86" ]

After:

nix-repl> legacyPackages.x86_64-linux.cudaPackages_11_8.cudaFlags.cudaGencode
[ "-gencode=arch=compute_35,code=sm_35" "-gencode=arch=compute_50,code=sm_50" "-gencode=arch=compute_52,code=sm_52" "-gencode=arch=compute_60,code=sm_60" "-gencode=arch=compute_61,code=sm_61" "-gencode=arch=compute_70,code=sm_70" "-gencode=arch=compute_75,code=sm_75" "-gencode=arch=compute_80,code=sm_80" "-gencode=arch=compute_86,code=sm_86" "-gencode=arch=compute_86,code=compute_86" ]

Specifically, "-gencode=arch=compute_compute_86,code=compute_compute_86" becomes "-gencode=arch=compute_86,code=compute_86", which is a valid architecture per https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/#gpu-name-gpuname-arch.

Must be merged prior to #215549.

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/)
• 23.05 Release Notes (or backporting 22.11 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.

cc @NixOS/cuda-maintainers @cuda-maintainers

[ConnorBaker]

Result of nixpkgs-review pr 215552 run on x86_64-linux 1

[ConnorBaker]

I don't understand why this rebuilt nothing given the flags changed.

[ConnorBaker]

I can confirm that this fix allows NCCL to build when using cudaFlags: #215549.

[ConnorBaker]

Bundling into #215229.