$ cat src/lib.rs
extern "C" {
    fn xsave64(p: *mut u8, hi: u32, lo: u32)
        -> /* comment */ ();
}
$ cargo +nightly clippy --fix  -Z unstable-options
$ git diff
diff --git a/src/lib.rs b/src/lib.rs
index e07dbbc..0110132 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,6 @@
 extern "C" {
     fn xsave64(p: *mut u8, hi: u32, lo: u32)
-        -> /*comment here*/ ();
+        ;
 }