Rollup merge of #40703 - GuillaumeGomez:pointer-docs, r=steveklabnik

Add missing urls in ptr docs

r? @rust-lang/docs

src/libstd/primitive_docs.rs

@@ -183,9 +183,9 @@ mod prim_unit { }
 /// Working with raw pointers in Rust is uncommon,
 /// typically limited to a few patterns.
 ///
-/// Use the `null` function to create null pointers, and the `is_null` method
+/// Use the [`null`] function to create null pointers, and the [`is_null`] method
 /// of the `*const T` type  to check for null. The `*const T` type also defines
-/// the `offset` method, for pointer math.
+/// the [`offset`] method, for pointer math.
 ///
 /// # Common ways to create raw pointers
 ///
@@ -213,7 +213,7 @@ mod prim_unit { }
 ///
 /// ## 2. Consume a box (`Box<T>`).
 ///
-/// The `into_raw` function consumes a box and returns
+/// The [`into_raw`] function consumes a box and returns
 /// the raw pointer. It doesn't destroy `T` or deallocate any memory.
 ///
 /// ```
@@ -227,7 +227,7 @@ mod prim_unit { }
 /// }
 /// ```
 ///
-/// Note that here the call to `drop` is for clarity - it indicates
+/// Note that here the call to [`drop`] is for clarity - it indicates
 /// that we are done with the given value and it should be destroyed.
 ///
 /// ## 3. Get it from C.
@@ -255,6 +255,11 @@ mod prim_unit { }
 ///
 /// *[See also the `std::ptr` module](ptr/index.html).*
 ///
+/// [`null`]: ../std/ptr/fn.null.html
+/// [`is_null`]: ../std/primitive.pointer.html#method.is_null
+/// [`offset`]: ../std/primitive.pointer.html#method.offset
+/// [`into_raw`]: ../std/boxed/struct.Box.html#method.into_raw
+/// [`drop`]: ../std/mem/fn.drop.html
 #[stable(feature = "rust1", since = "1.0.0")]
 mod prim_pointer { }