[dcl.constexpr] Make cross-reference for "encloses" more precise.

Author: zygoloid

source/declarations.tex

@@ -837,7 +837,7 @@
 its class shall not have any virtual base classes;
 
 \item
-its \grammarterm{function-body} shall not enclose\iref{stmt.stmt}
+its \grammarterm{function-body} shall not enclose\iref{stmt.pre}
 \begin{itemize}
 \item a \tcode{goto} statement,
 \item an identifier label\iref{stmt.label},