Closes #269548 NixOS/nix#9640 by incorporating upstream fix: llvm/llvm-project#77218

This change fixes segfaults when multiple c++ libraries are loaded -- this happens on older macos release, eg: big sur, where the system libc++ is loaded as part of the framework, or newer macos, eg: monterey, when one libc++ library is loaded at init and some other libc++ is dlopened later.

The problem stems from not linking with the -Wl,-force_symbols_not_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/../lib/notweak.exp flags which are defined only when LIBCXX_CXX_ABI=libcxxabi in the CMakeLists.txt. These link flags were defined in nixpkgs prior to llvmPackages_15. llvmPackages_15 started using system-libcxxabi, which was introduced https://reviews.llvm.org/D119539 and refined https://reviews.llvm.org/D120727, rather than just libcxxabi.

The upstream fix llvm/llvm-project#77218 treats libcxxabi and system-libcxxabi the same so both get the correct linker flags when built on darwin hosts.

testing:

nix-shell -I nixpkgs=. -p nix --run 'nix-shell -I nixpkgs=. -p ponysay --dry-run'

# shell.nix
{pkgs ? import <nixpkgs> {}}:
let
  dltest = pkgs.callPackage (
    { lib
    , runCommandCC
    , writeText
    , libcxx
    }:
    let
      name = "dltest";
      code = writeText "${name}.c" ''
        #include <dlfcn.h>
        #include <stdio.h>

        int
        main(int argc, const char **argv)
        {
            int numFailed = 0;
            for (int i = 1; i < argc; i++) {
              int failed = dlopen(argv[i], RTLD_LOCAL | RTLD_LAZY) == 0;
              numFailed += failed;
              fprintf(stderr, "dlopen %s: %s\n", argv[i], failed ? "failed" : "succeeded");
            }
            return numFailed;
        }
      '';
    in
      runCommandCC name {src = code;} ''
        mkdir -p "$out"/bin
        cc -Wall -Werror -O2 -o "$out/bin/${name}" "$src" -ldl -L${lib.getLib libcxx}/lib -lc++
      ''
  ) {
    libcxx = pkgs.llvmPackages_16.libcxx;
  };

  shell =
  let
    inherit (pkgs) lib stdenv mkShell writeShellScriptBin;
    ext = stdenv.hostPlatform.extensions.sharedLibrary;
    libcxx-16 = pkgs.llvmPackages_16.libcxx;
    libcxx-15 = pkgs.llvmPackages_15.libcxx;
    getLibcxx = libcxx: "${lib.getLib libcxx}/lib/libc++${ext}" + lib.optionalString stdenv.isLinux ".1";
  in
    mkShell {
      packages = [
        dltest
        (writeShellScriptBin "runtests" ''
          DYLD_PRINT_INITIALIZERS=1 ${lib.getBin dltest}/bin/dltest \
            ${getLibcxx libcxx-15} \
            ${getLibcxx libcxx-16}
        '')
      ];
      shellHook = "runtests";
    };
in
  shell

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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this change is the result of contributions from:
@abathur @cormacrelf @reckenrode @veprbl