Uplift rustfmt macro formatting fix

[Manishearth]

This uplifts the fix for rust-lang/rustfmt#6985 (rust-lang/rustfmt#6990), which is a rustfmt ICE breaking multiple crates.

This should be backported to beta.

[rustbot]

rustfmt is developed in its own repository. If possible, consider making this change to rust-lang/rustfmt instead.

cc @rust-lang/rustfmt

[rustbot]

r? @jieyouxu

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: rustfmt, rustfmt-contributors
• rustfmt, rustfmt-contributors expanded to 6 candidates
• Random selection from fee1-dead, jieyouxu, ytmimi

[ytmimi]

@Manishearth you can r=me once CI is green

[Manishearth]

@bors r=ytmimi

[rust-bors]

📌 Commit d827d44 has been approved by ytmimi

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 10. This pull request will be tested once the tree is reopened.

Reason for tree closure: To keep an eye on