Add tests for doc attribute check

Author: GuillaumeGomez

src/test/rustdoc-ui/doc-attr.rs

@@ -0,0 +1,5 @@
+#![crate_type = "lib"]
+#![doc(as_ptr)] //~ ERROR
+
+#[doc(as_ptr)] //~ ERROR
+pub fn foo() {}

src/test/rustdoc-ui/doc-attr.stderr

@@ -0,0 +1,14 @@
+error: unknown `doc` attribute `as_ptr`
+  --> $DIR/doc-attr.rs:4:7
+   |
+LL | #[doc(as_ptr)]
+   |       ^^^^^^
+
+error: unknown `doc` attribute `as_ptr`
+  --> $DIR/doc-attr.rs:2:8
+   |
+LL | #![doc(as_ptr)]
+   |        ^^^^^^
+
+error: aborting due to 2 previous errors
+

src/test/ui/attributes/doc-attr.rs

@@ -0,0 +1,5 @@
+#![crate_type = "lib"]
+#![doc(as_ptr)] //~ ERROR
+
+#[doc(as_ptr)] //~ ERROR
+pub fn foo() {}

src/test/ui/attributes/doc-attr.stderr

@@ -0,0 +1,14 @@
+error: unknown `doc` attribute `as_ptr`
+  --> $DIR/doc-attr.rs:4:7
+   |
+LL | #[doc(as_ptr)]
+   |       ^^^^^^
+
+error: unknown `doc` attribute `as_ptr`
+  --> $DIR/doc-attr.rs:2:8
+   |
+LL | #![doc(as_ptr)]
+   |        ^^^^^^
+
+error: aborting due to 2 previous errors
+