clang, cc-wrapper: Move --gcc-toolchain logic into CC wrapper

[Ericson2314]

Motivation for this change

The new condition is slightly different, but I think it's OK?

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[Mic92]

It is intended to have this on macOS?

[Ericson2314]

On macOS libcxx != null so it shouldn't. On the other hand it might be needed with libcxxClang and not have it.

We might need to also make cc-wrapper libgcc/compiler-rt aware (something we probably should do in general) to fix that case if it is indeed messed up for libcxxClang.

[Mic92]

Ok. I was just asking if there is a libgcc based stdenv for macOS like their is a libcxx stdenv for Linux.

[Ericson2314]

Ah. I don't think there is. If there was it probably would use --gcc-toolchain. (When build finally build all the GCC libraries in separate derivations, this will be much easier!)

[Mic92]

Sounds good.

[LnL7]

There is a gccStdenv, which doesn't seem to use libc++ from what I can tell. I'm not sure what the implications of this flag are or if the condition triggers however.

HARDENING: disabled flags: pie
HARDENING: Is active (not completely disabled with "all" flag)
HARDENING: enabling fortify
HARDENING: enabling stackprotector
HARDENING: enabling strictoverflow
HARDENING: enabling format
HARDENING: enabling pic
extra flags before to /nix/store/q8ar8q8f2h4sq5563pcn9dnv7a8n8gns-gcc-9.3.0/bin/g++:
  -O2
  -D_FORTIFY_SOURCE=2
  -fstack-protector-strong
  --param
  ssp-buffer-size=4
  -fno-strict-overflow
  -Wformat
  -Wformat-security
  -Werror=format-security
  -fPIC
  -Wl\,-sdk_version
  -Wl\,10.12
  -Wl\,-no_uuid
original flags to /nix/store/q8ar8q8f2h4sq5563pcn9dnv7a8n8gns-gcc-9.3.0/bin/g++:
  -o
  hello
  hello.cc
extra flags after to /nix/store/q8ar8q8f2h4sq5563pcn9dnv7a8n8gns-gcc-9.3.0/bin/g++:
  -B/nix/store/fikpi6kfpfywadbqnrn6ldwif2glqvii-gcc-9.3.0-lib/lib
  -B/nix/store/i09q4si3r6ad3iblrdjxfmvl8bks6amg-Libsystem-osx-10.12.6/lib/
  -idirafter
  /nix/store/i09q4si3r6ad3iblrdjxfmvl8bks6amg-Libsystem-osx-10.12.6/include
  -idirafter
  /nix/store/q8ar8q8f2h4sq5563pcn9dnv7a8n8gns-gcc-9.3.0/lib/gcc/x86_64-apple-darwin/9.3.0/include-fixed
  -B/nix/store/nsq53ag0qb8q8ljxdwfxnm3k4ssbwqcf-gcc-wrapper-9.3.0/bin/
  -isystem
  /nix/store/29sdvdbaj16kxgzhxj72pa1dn3vrf9bw-clang-7.1.0/include
  -isystem
  /nix/store/29sdvdbaj16kxgzhxj72pa1dn3vrf9bw-clang-7.1.0/include
  -L/nix/store/29sdvdbaj16kxgzhxj72pa1dn3vrf9bw-clang-7.1.0/lib
  -L/nix/store/3z5szay7ax2p102ysnx8sgq8d305mp06-clang-7.1.0-lib/lib
  -L/nix/store/29sdvdbaj16kxgzhxj72pa1dn3vrf9bw-clang-7.1.0/lib
  -L/nix/store/3z5szay7ax2p102ysnx8sgq8d305mp06-clang-7.1.0-lib/lib
  -L/nix/store/i09q4si3r6ad3iblrdjxfmvl8bks6amg-Libsystem-osx-10.12.6/lib
  -L/nix/store/fikpi6kfpfywadbqnrn6ldwif2glqvii-gcc-9.3.0-lib/lib

[Ericson2314]

OK I rebased this, and added a isLinux condition to hew close to what we had before at the cost of some extra complexity, a long with a comment explaining the situation and how we might fix it better.

[vcunat]

This PR was reverted (for now). Unfortunately it isn't possible to reopen the original PR, but you can create a new one.