postgresqlPackages.vectorchord: fix build with rustc 1.96

[CertainLach]

Build fails on rustc 1.96, fix submitted upstream: supervc-stack/VectorChord#467

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.
• Follows the automation/AI policy.

[CertainLach]

Something is wrong here, it still fails to build as a part of nixpkgs

[CertainLach]

LLVM does some weird things with hardenings used by nixpkgs...

[CertainLach]

Patch I submitted to VectorChord fixes the individual crate build, but then fat lto during the full extension build breaks it back
Disabling hardening works fine here, so I believe some of them are causing a miscompilation

[CertainLach]

Ok, this was hard, but seems like I found the source of the problem :D
Described this in #staging:nixos.org matrix:

There is a mismatch in versions of llvm we bundle with rustc in nixpkgs, and upstream rustc (e.g oxalica rust-overlay) expects

rustc packaged at staging-next expects llvm to be built with this fix: rust-lang/llvm-project@94e2c19
It is included in official release of rustc 1.96, but is missing from nixpkgs rustc 1.96 as it is using system llvm without this fix

Simple reproducer I found is:

use std::arch::x86_64::{_mm512_dpbusd_epi32,__m512i};
#[target_feature(enable = "avx512vnni")]
pub unsafe fn dp(a:__m512i,b:__m512i,c:__m512i)->__m512i{_mm512_dpbusd_epi32(a, b, c)}

You can build this code on godbolt's rustc 1.96/with oxalica's rust-overlay, but nixpkgs rustc fails to build it with "rustc-LLVM ERROR: Cannot select: intrinsic %llvm.x86.avx512.vpdpbusd.512" error"

[diogotcorreia]

@CertainLach Do you have a PR/issue that tracks that problem? I'm interested in knowing if there is still something we need to do on the vectorchord package itself