COMP: Define ExceptionObject destructor out-of-line (doing Rule of Five)

Followed the C++ Rule of Five, instead of the Rule of Zero, for
`ExceptionObject`, and added the definition of its destructor to its CXX
file.

Aims to fix Visual C++ link errors (error LNK2005 "symbol was defined
more than once", fatal error LNK1169) reported by Simon Rit, and
confirmed by Lucas Gandel, at "Modernize the implementation of
ExceptionObject", pull request InsightSoftwareConsortium#2374

Modules/Core/Common/include/itkExceptionObject.h

@@ -50,12 +50,7 @@ class ITKCommon_EXPORT ExceptionObject : public std::exception
   static constexpr const char * const default_exception_message = "Generic ExceptionObject";
   using Superclass = std::exception;
 
-  /** Explicitly-defaulted default-constructor. Creates an empty exception object.
-   * \note The other five "special member functions" (copy-constructor,
-   * copy-assignment operator, move-constructor, move-assignment operator,
-   * and destructor) are defaulted implicitly, following the C++ "Rule of Zero".
-   * All of these special member functions are `noexcept`.
-   */
+  /** Explicitly-defaulted default-constructor. Creates an empty exception object. */
   ExceptionObject() noexcept = default;
 
   explicit ExceptionObject(const char * file,
@@ -67,6 +62,24 @@ class ITKCommon_EXPORT ExceptionObject : public std::exception
                            std::string  desc = "None",
                            std::string  loc = "Unknown");
 
+  /** Copy-constructor. */
+  ExceptionObject(const ExceptionObject &) noexcept = default;
+
+  /** Move-constructor. */
+  ExceptionObject(ExceptionObject &&) noexcept = default;
+
+  /** Copy-assignment operator. */
+  ExceptionObject &
+  operator=(const ExceptionObject &) noexcept = default;
+
+  /** Move-assignment operator. */
+  ExceptionObject &
+  operator=(ExceptionObject &&) noexcept = default;
+
+  /** Destructor.
+   * \note It appears necessary to define the destructor "out-of-line" for external linkage. */
+  ~ExceptionObject() override;
+
   /** Equivalence operator. */
   virtual bool
   operator==(const ExceptionObject & orig) const;

Modules/Core/Common/src/itkExceptionObject.cxx

@@ -75,6 +75,10 @@ ExceptionObject::ExceptionObject(std::string file, unsigned int lineNumber, std:
 {}
 
 
+// Note: It appears necessary to define the destructor "out-of-line" for external linkage.
+ExceptionObject::~ExceptionObject() = default;
+
+
 bool
 ExceptionObject::operator==(const ExceptionObject & orig) const
 {