Fix a comment.

nnethercote · nnethercote · commit 67e4bec200d9 · 2023-07-31T16:21:02.000+10:00
Make it match the corresponding comment at the start of the unstable
options.
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
@@ -1881,6 +1881,7 @@ written to standard error output)"),
 
     // If you add a new option, please update:
     // - compiler/rustc_interface/src/tests.rs
+    // - src/doc/unstable-book/src/compiler-flags
 }
 
 #[derive(Clone, Hash, PartialEq, Eq, Debug)]

Original file line number	Diff line number	Diff line change
`@@ -1881,6 +1881,7 @@ written to standard error output)"),`
`1881`	`1881`
`1882`	`1882`	`// If you add a new option, please update:`
`1883`	`1883`	`// - compiler/rustc_interface/src/tests.rs`
	`1884`	`+ // - src/doc/unstable-book/src/compiler-flags`
`1884`	`1885`	`}`
`1885`	`1886`
`1886`	`1887`	`#[derive(Clone, Hash, PartialEq, Eq, Debug)]`