`./x fmt --all` is not idempotent

[jieyouxu]

In the use formatting PR #125443 it was noticed that ./x fmt --all was not idempotent, i.e. ./x fmt --all had to be run twice to reproduce the formatted diff.

(I tried looking for an existing issue for this but couldn't find one.)

[Kobzol]

This is not an issue of ./x fmt --all, but of rustfmt. It is not idempotent on this file.

Local repro:

$ ./build/x86_64-unknown-linux-gnu/rustfmt/bin/rustfmt --config-path ${PWD} --edition 2021 --unstable-features --skip-children library/std/src/os/fortanix_sgx/mod.rs
md5sum library/std/src/os/fortanix_sgx/mod.rs
afac84de68b9a8f072adee0b28d1a0d4  library/std/src/os/fortanix_sgx/mod.rs
$ ./build/x86_64-unknown-linux-gnu/rustfmt/bin/rustfmt --config-path ${PWD} --edition 2021 --unstable-features --skip-children library/std/src/os/fortanix_sgx/mod.rs
893f3e29999121b7efb0251662ded8f2  library/std/src/os/fortanix_sgx/mod.rs

[Kobzol]

Filed an issue in rustfmt: rust-lang/rustfmt#6195.