Fix todo comments about testing

[khyperia]

Three todo comments that I found with a quick grep:

https://github.com/EmbarkStudios/rust-gpu/blob/06fdb85d61237725bc23a72c8d18142ffcbc4391/rustc_codegen_spirv/src/builder/intrinsics.rs#L336

https://github.com/EmbarkStudios/rust-gpu/blob/06fdb85d61237725bc23a72c8d18142ffcbc4391/rustc_codegen_spirv/src/builder/mod.rs#L170

https://github.com/EmbarkStudios/rust-gpu/blob/06fdb85d61237725bc23a72c8d18142ffcbc4391/rustc_codegen_spirv/src/builder/builder_methods.rs#L262

I don't actually know how to set up a test harness to be able to run these on CI, but, oh well, we can figure that out as we go.

[khyperia]

Also copysign, implemented in https://github.com/EmbarkStudios/rust-gpu/pull/158

[khyperia]

IIRC we talked about this a long time ago @XAMPPRocky and you said you'd like to work on it and that's why I assigned you, but at this point I've completely forgotten - do you still plan on doing this, or would you like to just close this?

[XAMPPRocky]

I can still work on it if it's important. What would the way to add a test for this? I'm assuming we'd add unit tests in rustc_codegen_spirv?

[khyperia]

It's not important at all :P the tests probably wouldn't be in rustc_codegen_spirv, since the thing I want to test is if it executes correctly - I have no idea if that splat of instructions actually does what it's supposed to be doing (testing if they're emitted correctly isn't really relevant or important)

[oisyn]

Closing this due to being very old 😉. There's definitely more // TODO's in the code that we should address at some point.