[Don't merge][test] mir niche checks

[dianqk]

This PR is used to test #104862.
Upstream patch: llvm/llvm-project#68190.
Discussion: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Implementing.20niche.20checks.

r? saethlin

[rustbot]

⚠️ Warning ⚠️

• These commits modify submodules.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino

The Miri subtree was changed

cc @rust-lang/miri

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

[rustbot]

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

The Miri subtree was changed

cc @rust-lang/miri

[saethlin]

@dianqk If you want to get CI to pass with the MIR transform in here, you probably need to add -Zmir-enable-passes=-CheckNiches or -Cdebug-assertions=no to the tests that are failing due to perturbation by the check.

[dianqk]

I just remembered that x86_64-gnu-llvm-15 and x86_64-gnu-tools do not use the built-in LLVM.

[dianqk]

Verify completion.

[dianqk]

Check again due to the reimplementation of the upstream patch.