Disable rounding intrinsics

[adpaco]

Description of changes:

Disables rounding intrinsics which appear to be replaced by assert-false statements for some reason (debugging will come later). We could leave them "as is", but in my opinion we should control how they behave for now and only enable them when they are fixed and tested.

Resolved issues:

Part of #727

Call-outs:

Testing:

• How is this change tested? Adds 6 negative tests.

• Is this a refactor change? No.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[zhassan-aws]

Disabling them until they're fixed sounds like the right thing to me. Should we replace their implementations with:

codegen_unimplemented_intrinsic!(
                "https://github.com/model-checking/kani/issues/1025"

though?

[adpaco]

Should we replace their implementations with:

codegen_unimplemented_intrinsic!(
                "https://github.com/model-checking/kani/issues/1025"

though?

Yes, thanks! It's done.