fix link

Author: Vladimir Kotal

threads.tex

@@ -595,7 +595,7 @@
 cleanup. In fact, more often than not these functions are implemented as macros
 that open and close code blocks. This enforces this usage pattern
 (and causes trouble with \texttt{goto} statements).
-\item Run a C preprocessor on \example{pthreads/pthread-create.c} and see how
+\item Run a C preprocessor on \example{pthreads/pthread-cleanup.c} and see how
 this is done.
 \end{itemize}