add compiletest headers to rustdoc-gui tests

tests/rustdoc-gui/source-anchor-scroll.goml

@@ -8,13 +8,13 @@ set-window-size: (600, 800)
 assert-property: ("html", {"scrollTop": "0"})
 
 click: '//a[text() = "barbar"]'
-assert-property: ("html", {"scrollTop": "125"})
+assert-property: ("html", {"scrollTop": "149"})
 click: '//a[text() = "bar"]'
-assert-property: ("html", {"scrollTop": "156"})
+assert-property: ("html", {"scrollTop": "180"})
 click: '//a[text() = "sub_fn"]'
-assert-property: ("html", {"scrollTop": "53"})
+assert-property: ("html", {"scrollTop": "77"})
 
 // We now check that clicking on lines doesn't change the scroll
 // Extra information: the "sub_fn" function header is on line 1.
 click: '//*[@id="6"]'
-assert-property: ("html", {"scrollTop": "53"})
+assert-property: ("html", {"scrollTop": "77"})

tests/rustdoc-gui/src/extend_css/lib.rs

+// compile-flags: --extend-css extra.css
 //! <div class="extend">text in red</div>

tests/rustdoc-gui/src/link_to_definition/lib.rs

+// compile-flags: -Zunstable-options --generate-link-to-definition
 pub fn sub_fn() {
     barbar();
 }

tests/rustdoc-gui/src/scrape_examples/src/lib.rs

+// run-flags:-Zrustdoc-scrape-examples
 /// # Examples
 ///
 /// ```