force libm <=0.2.11, as 0.2.12 has breaking changes

[Firestar99]

closes #242

[tgross35]

Would you clarifying the problem is? 0.2.12 was not a breaking changes.

[Firestar99]

Wrote you a summary in #242

libm 0.2.12+ breaks rust-gpu due to introducing new intrinsics that interact with rustc. We have a bit of a weird way to process these intrinsics and emit the corresponding SPIR-V (potentially with GLSL extensions) that needs to be updated to understand these new intrinsics. For now, we're locking libm to 0.2.11 to prevent new projects or cargo update from picking up newer broken versions.

[nazar-pc]

Well, I really don't like the solution of constraining the version here because it is toxic for downstream users that at some point will be unable to upgrade their dependencies due to conflicts.

There is also no TODO or any explanation in the Cargo.toml explaining what the issue is and what it would take to lift it. Consider always leaving one with a link to issue/discussion for future reference. I also don't see a linked issue about removing this requirement in general. This can't be a long-term solution.