Missing type error on function pointers with different ABIs

I tried this code: https://github.com/rust-lang/rust/blob/aa3ca1994904f2e056679fce1f185db8c7ed2703/src/test/ui/issue-10764.rs

fn f(_: extern "Rust" fn()) {}
extern fn bar() {}

fn main() { f(bar) }
//~^ ERROR mismatched types

I expected to see this happen: //~^ ERROR mismatched types

Instead, this happened:

<source>:1:9: error: unknown ABI option
    1 | fn f(_: extern "Rust" fn()) {}
      |         ^~~~~~

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• What version of Rust GCC were you using, git sha if possible. be27571c110d99fe55324a9c2b6622787b08fb52

Start with the reproduction in src/test/ui/issue-10764.rs at the referenced commit and run it through gccrs to confirm the current diagnostic. Trace how the compiler handles the extern "Rust" ABI and function-pointer type checking; done means the example reports the expected mismatched types error instead of unknown ABI option.