Rollup merge of rust-lang#38674 - GuillaumeGomez:atomic_fn_docs, r=frewsxcv

Add missing urls for atomic fn docs

r? @frewsxcv

Author: alexcrichton

src/libcore/sync/atomic.rs

@@ -1495,24 +1495,31 @@ unsafe fn atomic_xor<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// An atomic fence.
 ///
-/// A fence 'A' which has `Release` ordering semantics, synchronizes with a
-/// fence 'B' with (at least) `Acquire` semantics, if and only if there exists
+/// A fence 'A' which has [`Release`] ordering semantics, synchronizes with a
+/// fence 'B' with (at least) [`Acquire`] semantics, if and only if there exists
 /// atomic operations X and Y, both operating on some atomic object 'M' such
 /// that A is sequenced before X, Y is synchronized before B and Y observes
 /// the change to M. This provides a happens-before dependence between A and B.
 ///
-/// Atomic operations with `Release` or `Acquire` semantics can also synchronize
+/// Atomic operations with [`Release`] or [`Acquire`] semantics can also synchronize
 /// with a fence.
 ///
-/// A fence which has `SeqCst` ordering, in addition to having both `Acquire`
-/// and `Release` semantics, participates in the global program order of the
-/// other `SeqCst` operations and/or fences.
+/// A fence which has [`SeqCst`] ordering, in addition to having both [`Acquire`]
+/// and [`Release`] semantics, participates in the global program order of the
+/// other [`SeqCst`] operations and/or fences.
 ///
-/// Accepts `Acquire`, `Release`, `AcqRel` and `SeqCst` orderings.
+/// Accepts [`Acquire`], [`Release`], [`AcqRel`] and [`SeqCst`] orderings.
 ///
 /// # Panics
 ///
-/// Panics if `order` is `Relaxed`.
+/// Panics if `order` is [`Relaxed`].
+///
+/// [`Ordering`]: enum.Ordering.html
+/// [`Acquire`]: enum.Ordering.html#variant.Acquire
+/// [`SeqCst`]: enum.Ordering.html#variant.SeqCst
+/// [`Release`]: enum.Ordering.html#variant.Release
+/// [`AcqRel`]: enum.Ordering.html#variant.AcqRel
+/// [`Relaxed`]: enum.Ordering.html#variant.Relaxed
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn fence(order: Ordering) {