Fix spacing of pretty printed const item without body

[dtolnay]

Follow-up to #92238 fixing one of the FIXMEs.

macro_rules! repro {
    ($item:item) => {
        stringify!($item)
    };
}

fn main() {
    println!("{}", repro!(extern "C" { static S: i32; }));
}

Before: extern "C" { static S: i32 ; }
After: extern "C" { static S: i32; }

[rust-highfive]

r? @oli-obk

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[oli-obk]

@bors r+ rollup

[bors]

📌 Commit b621635 has been approved by oli-obk