Update nix-build.cc: don't add gcc automatically

[phip1611]

Motivation

nix-shell -p gcc13 --run "gcc --version" always prints the version of gcc12, the current default gcc. This doesn't work as expected. In a flake shell however, it works as expected.

With this change, this doesn't happen anymore.

Context

This changes arises from this upstream discussion:

NixOS/nixpkgs#283248 (comment)

I didn't test this but it looks as it would work.

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[roberth]

nix-shell -p should never have been hardcoded into Nix, because changes like this will break some users' shells when they update Nix. That's not how Nix is supposed to work.
I think this behavior should be behind a --no-cc flag for that reason.
Long term, we want to empower Nixpkgs and other expressions to provide such behavior; e.g.

• Allow to get rid of nix develop "shell" logic #7501

--no-cc is obviously not great either, because it's something to be learned and easy to forget. Perhaps we could warn when one of the parameters starts with gcc or clang? That's terribly ad hoc, but such is the nature of nix-shell -p.

[edolstra]

I think we shouldn't change the legacy interface at this point. You can use nix shell, which doesn't include gcc.

[phip1611]

Makes sense. I'm just used to nix-shell :D

Thanks!

[szmarczak]

@phip1611 @roberth @edolstra The issue is that https://nixos.org/ does use nix-shell -p which is extremely confusing for newcomers. It shouldn't be that hard to use GCC 14. People might use Docker or some other distro and install brew instead...