Rollup merge of #141654 - durin42:randomly-fixed-test, r=jieyouxu

tests: mark option-niche-eq as fixed on LLVM 21

Some combination of recent Rust changes (between 3d86494a0d01 and aa57e46e24a4 from what I can tell) and changes in LLVM 21 (not recently, as best I can tell) have caused this test to start showing the behavior we want, so it's time to move this test to a proper place and mark it as fixed on LLVM 21.

~~Probably "fixes" rust-lang/rust#49892, but I'll let others make that call.~~

Closes rust-lang/rust#49892 unless we want to break out a dedicated issue for `Option<bool>::eq` on LLVM 20 (seems low-value).

`@rustbot` label llvm-main

Author: matthiaskrgr