libcxxabi: also install libc++abi.a

[Twey]

Motivation for this change

Allows building static binaries with libcxxStdenv. The file is only 536K in size, so it seems a waste to throw it away after building it.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• 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 nox --run "nox-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)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

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[Twey]

I haven't touched llvmPackages_3* because they look like they require more work — llvmPackages_3*.libcxx doesn't seem to build static libraries either.

[Mic92]

In glibc we have a static output. How about this one?

[matthewbauer]

I am not very supportive of static outputs. The issue is lots of things like pkgconfig hardcode the libdir. Instead, i would recommend adding an “enableStatic” argument that can be overriden.

[Twey]

I modeled this on libstdc++, which just bundles both static and non-static outputs into the gcc derivation.

The static library is pretty small and we were building it anyway and throwing it away. This is meant as a tiny patch that just allows us to build static libraries with libcxxStdenv, which was previously broken. I tried not to make any architectural decisions :)

[Twey]

The argument expected by makeStaticLibraries has a double negative — it's called dontDisableStatic. If we're going to add an argument to things, shouldn't we stick to that convention?

[twey@uruz:~/nix/nixpkgs]$ grep -Irc enableStatic | awk -F: '{ s += $2 } END { print s }'
49

[twey@uruz:~/nix/nixpkgs]$ grep -Irc dontDisableStatic | awk -F: '{ s += $2 } END { print s }'
52

There doesn't seem to be consensus 😆

[Twey]

But there are many more files with the double negative.

[twey@uruz:~/nix/nixpkgs]$ grep -Irl dontDisableStatic | wc -l
49

[twey@uruz:~/nix/nixpkgs]$ grep -Irl enableStatic | wc -l
19

[matthewbauer]

Yeah dontDisableStatic would be fine as well. The double negative is kind of awkward in my opinion though.

But yeah, this sounds okay if it's consistent with how we handle gcc.

[Twey]

I feel like it would be weird to have an enableStatic flag just for libc++abi. If anything it should go in libc++ — since static libc++ is useless without static libc++abi.

Are we okay to merge this?

[Mic92]

This should have not gone to master!