clang-tools: fix C++ include paths not being passed to tools

[yshui]

c++ standard library paths are passed to clang via -cxx-isystem, which is not handled by the wrapper script. therefore clangd just can't find c++ includes.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[yshui]

cc @Mic92 @cmm

[gregorburger]

Thanks for the fix; this seems to be affecting 25.11 as well.

[yshui]

Caused by 76a8ffa i think

[rebmit]

Is this a duplicate of #462747? That one has been merged, but hasn't reached unstable branch yet.

[GrahamDennis]

I agree, I think the root cause here is that #462747 needs to land to master but for whatever reason targeted staging.

[yshui]

Oh, i didnt' know the existence of #462747 . but that approach looks wrong. now cxx include paths are added to CPATH too, which might cause conflicts