[intro.races] Clarify conflicts for the case where no bits are changed

Author: eisenwave

source/basic.tex

@@ -6169,9 +6169,13 @@
 \end{note}
 
 \pnum
-Two expression evaluations \defn{conflict} if one of them modifies a memory
+Two expression evaluations \defn{conflict} if one of them modifies\iref{defns.access} a memory
 location\iref{intro.memory} and the other one reads or modifies the same
 memory location.
+\begin{note}
+When a modification alters no bits,
+this does not prevent if from conflicting.
+\end{note}
 
 \pnum
 The library defines a number of atomic operations\iref{atomics} and