Fix some old `// <directive>` to `//@ <directive>`

src/fuzzing.md

@@ -73,7 +73,7 @@ To build a corpus, you may want to use:
 
 - The rustc/rust-analyzer/clippy test suites (or even source code) --- though avoid
   tests that are already known to cause failures, which often begin with comments
-  like `// failure-status: 101` or `// known-bug: #NNN`.
+  like `//@ failure-status: 101` or `//@ known-bug: #NNN`.
 - The already-fixed ICEs in the archived [Glacier][glacier] repository --- though
   avoid the unfixed ones in `ices/`!
 

src/rustdoc-internals.md

@@ -281,10 +281,10 @@ using `XPath` notation to get a precise look at the output. The full
 description of all the commands available to `rustdoc` tests (e.g. [`@has`] and
 [`@matches`]) is in [`htmldocck.py`].
 
-To use multiple crates in a `rustdoc` test, add `// aux-build:filename.rs`
+To use multiple crates in a `rustdoc` test, add `//@ aux-build:filename.rs`
 to the top of the test file. `filename.rs` should be placed in an `auxiliary`
 directory relative to the test file with the comment. If you need to build
-docs for the auxiliary file, use `// build-aux-docs`.
+docs for the auxiliary file, use `//@ build-aux-docs`.
 
 In addition, there are separate tests for the search index and `rustdoc`'s
 ability to query it. The files in `tests/rustdoc-js` each contain a

src/tests/compiletest.md

@@ -619,7 +619,7 @@ file). The `-L` flag is used to find the extern crates.
 `aux-crate` is very similar to `aux-build`. However, it uses the `--extern` flag
 to link to the extern crate to make the crate be available as an extern prelude.
 That allows you to specify the additional syntax of the `--extern` flag, such as
-renaming a dependency. For example, `// aux-crate:foo=bar.rs` will compile
+renaming a dependency. For example, `//@ aux-crate:foo=bar.rs` will compile
 `auxiliary/bar.rs` and make it available under then name `foo` within the test.
 This is similar to how Cargo does dependency renaming.