[diff.cpp23.expr] Fix environment ("example" should be "codeblock")

Author: tkoeppe

source/compatibility.tex

@@ -24,12 +24,12 @@
 that relies on the result of pointer comparison between backing arrays
 may change behavior.
 For example:
-\begin{example}
+\begin{codeblock}
 bool ne(std::initializer_list<int> a, std::initializer_list<int> b) {
   return a.begin() != b.begin() + 1;
 }
-bool b = ne({2,3}, {1,2,3}); // unspecified result; previously \tcode{false}
-\end{example}
+bool b = ne({2,3}, {1,2,3});    // unspecified result; previously \tcode{false}
+\end{codeblock}
 
 \rSec2[diff.cpp23.strings]{\ref{strings}: strings library}