Q(Unhandled)Exception: declare dtor out-of-line

De-duplicates vtables and enables RTTI on this hierarchy.

This is esp. important for exception classes, as RTTI is used
to select the catch clause to handle the exception in-flight.

The issue is made a bit complicated by the fact that the
exception specification changed from C++98 to 11 and that C++98
clients require the empty throw() specification while we don't
want to introduce warnings for C++11 users.

Let's hope no compiler includes throw specs into the mangled
names.

Task-number: QTBUG-45582
Change-Id: If086c8c38fccdc2c9c7e2aa7a492192cc1f86a6c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/thread/qexception.cpp

@@ -107,6 +107,11 @@ QT_BEGIN_NAMESPACE
     \internal
 */
 
+QException::~QException()
+{
+    // must stay empty until ### Qt 6
+}
+
 void QException::raise() const
 {
     QException e = *this;
@@ -118,6 +123,11 @@ QException *QException::clone() const
     return new QException(*this);
 }
 
+QUnhandledException::~QUnhandledException()
+{
+    // must stay empty until ### Qt 6
+}
+
 void QUnhandledException::raise() const
 {
     QUnhandledException e = *this;

src/corelib/thread/qexception.h

@@ -53,6 +53,11 @@ QT_BEGIN_NAMESPACE
 class Q_CORE_EXPORT QException : public std::exception
 {
 public:
+    ~QException()
+#ifndef Q_COMPILER_NOEXCEPT
+    throw()
+#endif
+    ;
     virtual void raise() const;
     virtual QException *clone() const;
 };
@@ -60,6 +65,11 @@ public:
 class Q_CORE_EXPORT QUnhandledException : public QException
 {
 public:
+    ~QUnhandledException()
+#ifndef Q_COMPILER_NOEXCEPT
+    throw()
+#endif
+;
     void raise() const Q_DECL_OVERRIDE;
     QUnhandledException *clone() const Q_DECL_OVERRIDE;
 };