cc-wrapper: fix linking against GCC libs for non-GCC

[Kha]

Motivation for this change

clang++ currently links programs statically against libstdc++, which is not expected as upstream clang as well as g++ do not do so. It turns out that while gccForLibs.lib contains a libstdc++.so.6, the specified path does not exist (anymore?), so this change restores the likely intended behavior.
Without this change, clang finds a libstdc++.a by appending ../../.. to the -L flag above the changed line. Not sure where that is coming from, but with this change the flag order makes it find the .so first.

/cc @Ericson2314?

$ echo '#include <exception>\nint main() { throw std::exception(); }' > foo.cpp
$ nix shell nixpkgs#clang -c c++ foo.cpp
$ ldd a.out | grep libstd
$

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 packages 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/)
• 21.11 Release Notes (or backporting 21.05 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.

[SuperSandro2000]

@alyssais @Ericson2314 ping

[stale]

I marked this as stale due to inactivity. → More info

[NickCao]

Still relevant.

[andurillb]

How could I increase the level of urgency of this PR?

[danielfullmer]

I've submitted another PR for this issue which also works in the cross-compilation case: #192459