freshBootstrapTools: llvmPackages_11 -> llvmPackages_16

[ghost]

remove llvmPackages_11 reference in preparation to drop LLVM11

• split from treewide: drop LLVM11 #283591

need to figure out how to test...

• treewide: drop LLVM11 #283591 (comment)

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/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 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
• Fits CONTRIBUTING.md.

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[wegank]

Since this basically reverts 887d33a, is the issue in #241692 (comment) now resolved?

[toonn]

It doesn't actually revert my change. The problem was both llvmPackages_11 and llvmPackages (which is now llvmPackages_16) were used after the llvmPackages bump. So this is bumping it correctly.

The more important issue here, IMO, is this will make freshBootstrapTools differ from the actual bootstrap tools used. Now, that can be resolved by switching to these newly built bootstrap tools but that's exactly what we've been putting off until there's a strong enough motivation to do so. Let's batch any other bootstrap tools improvements together so we're not rebuilding the world over a more or less cosmetic change.

[ghost]

thanks for taking a look at this change! however, this is not just a cosmetic change. this is the last client of the LLVM11 toolchain, removing it will allow for dropping LLVM11 from nixpkgs which also moves forward in a step to simplifying the LLVM code as it removes one of the last LLVMs before it switched to a monorepo and unified libcxx / libcxxabi. If you're not aware there are issues with how we are building libcxx / libcxxabi which has resulted to segfaults when libcxx is loaded as well as having to specify libcxxabi when linking. when built together the build system properly re-exports the libcxxabi symbols from libcxx as well as marks the exported from libcxx as non-weak, fixing the segfault issue. (note, i've already committed a work around for the segfaulting libcxx).

• libcxx-{15,16,etc} segfault when multiple libcxx loaded #269548 (note that this effects all macos versions when multiple libcxx are loaded) llvmPackages_{15,16,17,git}.libcxx: use LIBCXX_CXX_ABI=libcxxabi link flags on darwin #278945
• Some libc++abi symbols are missing with LLVM12+'s stdenv on Darwin #166205

[ghost]

superseded by:

• stdenv.darwin: bootstrap darwin using updated tools #295558
• freshBootstrapTools: remove overlay, prune tools, use tar.xz archive #295557