STYLE: Declare lambda's created for Singleton const, but non-static

The lifetime of lambda's passed as argument to the function `Singleton<T>` does
not need to be extended beyond the function call, as these arguments directly
get converted to `std::function` objects.

Author: N-Dekker

Modules/Core/Common/include/itkSingletonMacro.h

@@ -44,11 +44,11 @@
   {                                                                                                 \
     if (m_##VarName == nullptr)                                                                     \
     {                                                                                               \
-      static auto setLambda = [](void * a) {                                                        \
+      const auto setLambda = [](void * a) {                                                         \
         delete m_##VarName;                                                                         \
         m_##VarName = static_cast<Type *>(a);                                                       \
       };                                                                                            \
-      static auto deleteLambda = []() {                                                             \
+      const auto deleteLambda = []() {                                                              \
         delete m_##VarName;                                                                         \
         m_##VarName = nullptr;                                                                      \
       };                                                                                            \

Modules/Core/Common/src/itkObjectFactoryBase.cxx

@@ -117,7 +117,7 @@ class ObjectFactoryBasePrivate : public LightObject
 ObjectFactoryBasePrivate *
 ObjectFactoryBase::GetPimplGlobalsPointer()
 {
-  static auto                deleteLambda = []() { m_PimplGlobals->UnRegister(); };
+  const auto                 deleteLambda = []() { m_PimplGlobals->UnRegister(); };
   ObjectFactoryBasePrivate * globalInstance =
     Singleton<ObjectFactoryBasePrivate>("ObjectFactoryBase", SynchronizeObjectFactoryBase, deleteLambda);
   if (globalInstance != m_PimplGlobals)