Add LLVM function pass test and LLVM module pass test

[frewsxcv]

To prevent #31067 from occurring again

At the time of writing, this is the only LLVM pass test we have in the suite:

https://github.com/rust-lang/rust/blob/master/src/test/auxiliary/llvm_pass_plugin.rs

which is testing a built-in pass and not a custom one.

[frewsxcv]

I'll take a stab at this