[coroutine.syn] Move "all freestanding" comment to the top

Author: tkoeppe

source/support.tex

@@ -5141,9 +5141,9 @@
 \indexheader{coroutine}%
 \indexlibraryglobal{noop_coroutine_handle}%
 \begin{codeblock}
+// all freestanding
 #include <compare>              // see \ref{compare.syn}
 
-// all freestanding
 namespace std {
   // \ref{coroutine.traits}, coroutine traits
   template<class R, class... ArgTypes>