vtkAtomicMutex: Define default destructor in declaration

warning: class 'vtkAtomicMutex' can be made trivially destructible by
defaulting the destructor on its first declaration [performance-trivially-destructible]

Common/Core/vtkAtomicMutex.cxx

@@ -32,9 +32,6 @@ vtkAtomicMutex::vtkAtomicMutex()
 {
 }
 
-//------------------------------------------------------------------------------
-vtkAtomicMutex::~vtkAtomicMutex() = default;
-
 //------------------------------------------------------------------------------
 vtkAtomicMutex::vtkAtomicMutex(const vtkAtomicMutex& other)
   : Locked(other.Locked.load(std::memory_order_acquire))

Common/Core/vtkAtomicMutex.h

@@ -35,7 +35,7 @@ class VTKCOMMONCORE_EXPORT vtkAtomicMutex
 public:
   // left public purposely to allow for copy construction
   vtkAtomicMutex();
-  ~vtkAtomicMutex();
+  ~vtkAtomicMutex() = default;
   vtkAtomicMutex(const vtkAtomicMutex& other);
   vtkAtomicMutex& operator=(const vtkAtomicMutex& other);