llvmPackages_{4,5}: musl compat

[dtzWill]

Fix llvm, clang, libcxxClang.

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-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/)
• Fits CONTRIBUTING.md.

---

Setting triples is part of one approach for enabling cross-compilation,
but for now only address native compilation and avoid rebuilds.

---

Prebuilt versions of these are available via cache.allvm.org if that's useful, details here: #34645 ("Quickstart with Binary Cache").

On Nix 2.0 you can probably use a temporary store or something to do this quickly without trusting the ALLVM cache system-wide...

[grahamc]

@GrahamcOfBorg eval

An eval issue was introduced in to master, sorry for the false failure.

[dtzWill]

0 rebuilds folks, you've got nothing to lose! 😈

[7c6f434c]

(looks carefully at the patches to find out the emergent interaction that will create a backdoor after some commit from LLVM repository lands in a 5.x release)

[7c6f434c]

@dtzWill but if you start using such an argument, shouldn't you ask for commit access (or maybe should have asked, some time ago)?

[dtzWill]

@7c6f434c yes, and it's been supported and passed along... probably should have pursued it a while back.

Regarding the 5.x changes--do you mean regarding the sharing of the patch? It just seemed to have a bit less clutter, but if that makes things harder to reason about or maintain I'm happy to do something else :).

In my local tree I just copied patches everywhere 😁.

Anyway, if that's not what you meant please clarify-- even if it's not something that needs addressing now never hurts to learn what others see as style considerations or whatnot :).

[7c6f434c]

It's not a style consideration, I just tried to imagine a situation where not changing anything currently built does not prevent the change from being unsafe in the long run.

[7c6f434c]

Re: access: I think you were asking for it wrong. @domenkozar @rbvermaa which of you is a better repository co-owner to ask?