core: Clang misses <optional> include

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>

diff --git a/src/common/async/detail/shared_mutex.h b/src/common/async/detail/shared_mutex.h
index 100ec701909f7ba42d4687984b42a6ac4df33b4a..1a79a69d4e14faf9807e502157ea1966a90b325b 100644 (file)
--- a/src/common/async/detail/shared_mutex.h
+++ b/src/common/async/detail/shared_mutex.h
@@ -16,6 +16,7 @@
 
 #include <condition_variable>
 #include <mutex>
+#include <optional>
 #include <shared_mutex> // for std::shared_lock
 
 #include <boost/smart_ptr/intrusive_ref_counter.hpp>