bees: replace uncaught_exception(), deprecated in C++17

uncaught_exception() had only the one valid use case, and it can be
reimplemented by literally calling current_exception() instead.

current_exception() has several valid use cases, so it is not likely
to be deprecated any time soon.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

lib/chatter.cc

@@ -146,7 +146,7 @@ namespace crucible {
 
 	ChatterUnwinder::~ChatterUnwinder()
 	{
-		if (uncaught_exception()) {
+		if (current_exception()) {
 			m_func();
 		}
 	}