Fix compiler errors with functions not returning values.

Core/src/Thread.cpp

@@ -34,6 +34,8 @@ TCThreadBase &TCThreadBase::operator=(const TCThreadBase &other) {
   // Our implementation is now the same as the other.
   m_Impl = other.m_Impl;
   m_Impl->IncreaseReferenceCount();
+
+  return *this;
 }
 
 TCThreadBase::~TCThreadBase() {

Core/src/ThreadGroup.cpp

@@ -243,6 +243,8 @@ bool ThreadGroup::CleanUpThreads() {
   // Reset active number of threads...
   m_ActiveThreads = 0;
   m_ExitFlag = false;
+
+  return true;
 }
 
 void ThreadGroup::Join() {