llvmPackages_39.stdenv cannot find libstdc++

[edolstra]

Issue description

In Nixpkgs 17.09, clang++ 3.9 cannot find libstdc++ headers:

$ nix-build -E 'with import <nixpkgs> {}; llvmPackages_39.stdenv.mkDerivation { name = "foo"; buildCommand = "echo \"#include <vector>\" > foo.cc; clang++ -c foo.cc -o $out"; }' -I nixpkgs=channel:nixos-17.09
these derivations will be built:
  /nix/store/m6cngdi7krryn25cm7bvgildpkjmi7bv-foo.drv
building path(s) '/nix/store/9c9dpbpdbkvpn1m8f6pgqzpygsxacw2j-foo'
building '/nix/store/m6cngdi7krryn25cm7bvgildpkjmi7bv-foo.drv'...
foo.cc:1:10: fatal error: 'vector' file not found
#include <vector>
         ^
1 error generated.
builder for '/nix/store/m6cngdi7krryn25cm7bvgildpkjmi7bv-foo.drv' failed with exit code 1
error: build of '/nix/store/m6cngdi7krryn25cm7bvgildpkjmi7bv-foo.drv' failed

This does work correctly with Clang 4.0 in 17.09, or Clang 3.9 in 17.03.

Setting NIX_DEBUG=1 shows that the cc-wrapper is not adding the appropriate -B flags pointing to libstdc++ in gcc.

Steps to reproduce

See above.

Technical details

• System: NixOS 17.03
• Nix version: 1.12pre
• Nixpkgs version: 17.09beta285.b50193f0ca
• Sandboxing enabled: no

[aristidb]

According to git-bisect, one of the following commits is causing the issue (all by @Ericson2314):

commit 2493454e13c25ff990d06deb38b1024e4a0a99f8 (refs/bisect/bad)
Author: John Ericson <John.Ericson@Obsidian.Systems>
Date:   Thu Aug 3 15:34:23 2017 -0400

    cc-wrapper: Use `set -u` throughout
    
    Now is an opportune time to do this, as the infixSalt conversion in
    `add-flags.sh` ensures that all the relevant `NIX_*` vars will be
    defined even if empty.

commit a8bd415fa06a100b29297db86aadb6f00da70bbf (refs/bisect/skip-a8bd415fa06a100b29297db86aadb6f00da70bbf)
Author: John Ericson <John.Ericson@Obsidian.Systems>
Date:   Thu Aug 3 11:29:15 2017 -0400

    unzip: cc-wrapper has been fixed so don't need to be so clever

commit 42f35503b56e293759685e9fb2a66ba75a55c339 (refs/bisect/skip-42f35503b56e293759685e9fb2a66ba75a55c339)
Author: John Ericson <John.Ericson@Obsidian.Systems>
Date:   Thu Jul 6 17:19:53 2017 -0400

    cc-wrapper: Make hygienic
    
    See the added comments for what exactly has been done.

commit 9f1e009975dc2d58541de435c74a26afe011542a (refs/bisect/skip-9f1e009975dc2d58541de435c74a26afe011542a)
Author: John Ericson <John.Ericson@Obsidian.Systems>
Date:   Mon Jun 26 00:43:06 2017 -0400

    cc-wrapper: Unconditionally use @infixSalt@ accross the board
    
    This is basically a sed job, in preparation of the next commit. The
    rules are more or less:
    
      - s"NIX_(.._WRAPPER_)?([a-zA-Z0-9@]*)"NIX_\1@infixSalt@_\2"g
    
      - except for non-cc-wrapper-specific vars like `NIX_DEBUG`

commit 5ba3972addac3dd56518da294d088c92a6fb9798 (refs/bisect/skip-5ba3972addac3dd56518da294d088c92a6fb9798)
Author: John Ericson <John.Ericson@Obsidian.Systems>
Date:   Mon Jun 26 00:43:06 2017 -0400

    cc-wrapper: Stop preWrapping
    
    This is an ugly temp hack for cross compilation, but now we have something better on the way.
    
    Bind `infixSalt` as an environment variable as it will be used in it.

[Ericson2314]

Hmm, #28998 was supposed to have fixed this, but I guess only fixed 4.0. @LnL7 any idea?

[LnL7]

Really thought I already applied those changes to the other versions, must have forgotten to push or something.

[Ericson2314]

Ah I see now---I should have noticed when reviewing that. While we're at it, maybe we should inject it in cc-wrapper instead of stdenv? This mirrors libcxxClang and keeps stdenvNoCC slimmer.