llvmPackages.clang: move add-nostdlibinc-flag.patch to cc-wrapper

[pwaller]

Remove a patch to decrease the divergence from upstream.

Motivation is a continuation of trying to reduce the number of clang
builds floating around. Wrapper builds are cheap, compiler builds are
not.

It's expected that this patch can be removed at some point and replaced
with some other cc-wrapper logic. This will be a little bit easier with
the logic already in the cc-wrapper.

Ongoing discussion in #191152. It would be nice to drop this but we
think it's probably needed at least on systems where /usr/include may be
available to prevent the possibility of picking up unwanted includes.

One potential method for eliminating nostdlibinc in the future is by
providing a non-existent -sysroot but that was reverted in #213185, and
remains a can of worms.

Signed-off-by: Peter Waller p@pwaller.net

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/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[emilazy]

Given that apparently the libc++ test case used to justify the LLVM patch previously now works without passing the flag at all (per discussion on Matrix), It would be good to verify if we actually need this. e.g., if we’re not passing it to GCC, is GCC currently leaky in the same way Clang would be without this flag? If so, then I don’t think it’s worth it to bother passing it at all, given the pitfalls.

cc @NixOS/llvm @NixOS/stdenv

[pwaller]

if we’re not passing it to GCC, is GCC currently leaky in the same way Clang would be without this flag? If so, then I don’t think it’s worth it to bother passing it at all, given the pitfalls.

strace -efile -f gcc -c test.c |& grep usr gives empty output, so I figure it has the -nostdlibinc-ish behaviour needed in the current nixpkgs build.

[emilazy]

Yay.

[pwaller]

Latest force removes extraneous blankline.

[emilazy]

Successfully built pkgsLLVM.hello and firefox on aarch64-linux, I think this is good to go.