Add type_traits include for `std::is_trivially_destructible`

(cherry picked from commit 3d46f2855860e93f1cd7d8cd73a35fe34bac64dd)

core/safe_refcount.h

@@ -36,6 +36,7 @@
 #if !defined(NO_THREADS)
 
 #include <atomic>
+#include <type_traits>
 
 // Design goals for these classes:
 // - No automatic conversions or arithmetic operators,