Failure to build ring for ios tests on rustc 1.91.0

[conradludgate]

First observed in this CI run, ios tests started failing when rustc updated to 1.91.0.

Confirmed locally on my macbook running

rustup target add aarch64-apple-ios-macabi --toolchain 1.90.0
cargo +1.90.0 test --target aarch64-apple-ios-macabi

rustup target add aarch64-apple-ios-macabi --toolchain 1.91.0
cargo +1.91.0 test --target aarch64-apple-ios-macabi

I'm guessing this is a regression in rustc, but raising this issue to track it accordingly.

[conradludgate]

bisected to nightly-2025-08-10

[conradludgate]

bisected to rust-lang/rust#139451, fixed in rust-lang/cc-rs#1517. Will make a PR to update cc.