Small ASIO fix to build in C++20

Author: andrewfb

include/asio/awaitable.hpp

@@ -25,6 +25,7 @@
 # include <experimental/coroutine>
 #endif // defined(ASIO_HAS_STD_COROUTINE)
 
+#include <utility>  // for std::exchange (needed in C++20)
 #include "asio/any_io_executor.hpp"
 
 #include "asio/detail/push_options.hpp"