cc-wrapper: add libcxx for libcxxClang

[matthewbauer]

clang needs to find headers + libraries for compiling with libc++. We
need to add a libcxx argument to cc-wrapper. This means you do not
have to pass in c++ headers directly.

This resolves the last case remaining of #30670. Darwin clang++ now
works properly.

Fixes #30670

[dtzWill]

Is this Darwin-only?

We previously had tests for this--were they failing? They seem to pass for me in my tree, FWIW.

I use libcxxStdenv for various things (including my system's nix) so I'm not sure what this is supposed to fix if it's not Darwin-only.

(regardless, is there a particular usage/scenario fixed by this? And should that be a test to ensure this works in the future?)

[matthewbauer]

This makes clang++ work outside of a Nix derivation... It's a kind of specific use case but was often an issue. We provide it for g++, so we might as well make it work with clang.

[aakropotkin]

Is this Darwin-only?

We previously had tests for this--were they failing? They seem to pass for me in my tree, FWIW.

I use libcxxStdenv for various things (including my system's nix) so I'm not sure what this is supposed to fix if it's not Darwin-only.

(regardless, is there a particular usage/scenario fixed by this? And should that be a test to ensure this works in the future?)

I completely agree, why does this not work on NixOS systems as well?
I am pulling my hair out just trying to hack around on a clang-c example.

I love NixOS but it's times like this that I get really frustrated with it...

I'm not always in the mood to write up a whole shell.nix for a little throwaway example; nix-shell -p clang or nix-shell -p llvmPackages.libclang should "work out the box".

JFC I'm not criticizing the author, I'm asking why this behavior is only for Darwin?

[Ericson2314]

It might be better since f3f7612

[Mic92]

Is this Darwin-only?
We previously had tests for this--were they failing? They seem to pass for me in my tree, FWIW.
I use libcxxStdenv for various things (including my system's nix) so I'm not sure what this is supposed to fix if it's not Darwin-only.
(regardless, is there a particular usage/scenario fixed by this? And should that be a test to ensure this works in the future?)

I completely agree, why does this not work on NixOS systems as well?
I am pulling my hair out just trying to hack around on a clang-c example.

I love NixOS but it's times like this that I get really frustrated with it...

I'm not always in the mood to write up a whole shell.nix for a little throwaway example; nix-shell -p clang or nix-shell -p llvmPackages.libclang should "work out the box".

JFC I'm not criticizing the author, I'm asking why this behavior is only for Darwin?

nix-shell -p clang would be nice to work until this happens you may find the following shell functions useful to improve your workflow: https://github.com/direnv/direnv/wiki/Nix#shell-function-to-quickly-setup-nix--direnv-in-a-new-project