Skip if_not_else lint for '!= 0'-style checks

[BenWiederhake]

Currently, clippy makes unhelpful suggestions such as this:

warning: unnecessary `!=` operation
   --> src/vm.rs:598:36
    |
598 |                     *destination = if source & 0x8000 != 0 { 0xFFFF } else { 0 };
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: change to `==` and swap the blocks of the `if`/`else`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_not_else
    = note: `-W clippy::if-not-else` implied by `-W clippy::pedantic`

Bit tests often take on the form if foo & 0x1234 != 0 { … } else { … }, and the != 0 part reads as "has any bits set". Therefore, this code already has the "correct" order, and shouldn't be changed.

This PR disables the lint for these cases, and in fact all cases where the condition is "foo is non-zero".

I did my homework:

• Followed [lint naming conventions][lint_naming] → Not applicable, this PR fixes an existing lint
• Added passing UI tests (including committed .stderr file) → Yes, tests/ui/if_not_else_bittest.rs
• cargo test passes locally
• Executed cargo dev update_lints
• Added lint documentation → Not applicable, this PR fixes an existing lint
• Run cargo dev fmt

changelog: Fix [if_not_else] false positive when something like bitflags != 0 is used

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @llogiq (or someone else) soon.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

• @rustbot author: the review is finished, PR author should check the comments and take action accordingly
• @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

[llogiq]

Ok, this seems like it should reduce the less useful messages from clippy, so thank you!

@bors r+

[bors]

📌 Commit 5e17f9f has been approved by llogiq

It is now in the queue for this repository.

[bors]

⌛ Testing commit 5e17f9f with merge f942470...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: llogiq
Pushing f942470 to master...