intrinsic-test fixes for low intrinsic, high core counts

[adamgemmell]

When the intrinsic count is low (such as when adding filtering for debugging) and the core count is high, sometimes the chunk count returned by manual_chunk() didn't match the number of modules created, which meant that the rust_programs/Cargo.toml referred to modules that didn't exist.

e.g. 100 intrinsics and 80 cores:
chunk_size = 100.div_ceil(80) = 2,
chunk count = 80

However, in practice, with a chunk_size of 2 Iter::chunks will only return 50 chunks. The fix is to calculate the real number of chunks with another div ceil, such as 100.div_ceil(2) = 50. There shouldn't be any difference when the intrinsic count is high enough for this to not matter.

In addition, this patch also adds the --tests argument to cargo test in order to not attempt running doc tests, which is a slowdown more noticeable with low intrinsic count and higher core count.

[rustbot]

r? @folkertdev

rustbot has assigned @folkertdev.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @Amanieu, @adamgemmell, @davidtwco, @folkertdev, @sayantn
• @Amanieu, @adamgemmell, @davidtwco, @folkertdev, @sayantn expanded to Amanieu, adamgemmell, davidtwco, folkertdev, sayantn
• Random selection from Amanieu, davidtwco, folkertdev, sayantn

[sayantn]

Is this just remnant from local trials?

View changes since the review

[adamgemmell]

No, adding --tests avoids attempting to run doc tests on each mod_n crate

[sayantn]

Oh ok I see. Thanks