rustc hangs with release build since the llvm 21 merge on crate not on crates.io

[Count-Count]

Steps to reproduce:

git clone -b v0.0.10 https://gitlab.wikimedia.org/countcount/wikimedia-eventstreams
cd wikimedia-eventstreams/
cargo +nightly build --release

Build hangs on last step. Bisected to dc0bae1

Works fine with 1.89 or non-release builds.

Sorry, but I don't have time to minimize right now, will try later if I find the time.

[Count-Count]

@rustbot label +I-hang +A-llvm

[nikic]

opt -passes=slp-vectorizer
https://gist.github.com/nikic/f12002e855c733cece331e9d4d2841f3

[nikic]

Upstream issue: llvm/llvm-project#155998