Due to a bug in LLVM 21, build fails on x86_64 with:
`rustc-LLVM ERROR: Cannot select: intrinsic %llvm.x86.avx512.vpdpbusd.512`.
This has been fixed in Rust's build of LLVM and LLVM 22 [1]
but this is not reflected in nixpkgs' packaging of rustc.
For this reason, we temporarily disable avx512vnni support until this is fixed in nixpkgs.
This might cause a performance penalty, but should not affect correctness.
See https://github.com/NixOS/nixpkgs/pull/537113#issuecomment-4846239887
[1]: 94e2c19f86
Those extensions don't support building with PostgreSQL 18, yet.
To make sure the broken status is updated on the next upgrade, they all
have version checks in the form of an evaluation warning, so that there
has be explicit action regarding its PG18 compatibility.