Fix intra-doc link

Author: GuillaumeGomez

src/librustdoc/doctest.rs

@@ -438,7 +438,7 @@ fn wrapped_rustc_command(rustc_wrappers: &[PathBuf], rustc_binary: &Path) -> Com
 /// (if multiple doctests are merged), `main` function,
 /// and everything needed to calculate the compiler's command-line arguments.
 /// The `# ` prefix on boring lines has also been stripped.
-struct RunnableDocTest {
+pub(crate) struct RunnableDocTest {
     full_test_code: String,
     full_test_line_offset: usize,
     test_opts: IndividualTestOptions,