[atomics.ref.pointer, atomics.types.memop] Add missing \tcode

Author: tkoeppe

source/threads.tex

@@ -4175,7 +4175,7 @@
 \pnum
 There are specializations of the \tcode{atomic_ref} class template
 for all pointer-to-object types.
-For each such type \placeholder{pointer-type},
+For each such type \tcode{\placeholder{pointer-type}},
 the specialization \tcode{atomic_ref<\placeholder{pointer-type}>} provides
 additional atomic operations appropriate to pointer types.
 
@@ -4373,10 +4373,10 @@
                           common to integers and pointers to objects}
 
 \pnum
-Let \placeholder{referred-type}
-be \placeholder{pointer-type}
+Let \tcode{\placeholder{referred-type}}
+be \tcode{\placeholder{pointer-type}}
 for the specializations in \ref{atomics.ref.pointer} and
-be \placeholder{integral-type}
+be \tcode{\placeholder{integral-type}}
 for the specializations in \ref{atomics.ref.int}.