Fix Issue 6423 - Garbage is returned from `void main()`
Merge pull request #3938 from yebblies/issue6423

Issue 6423 - Garbage is returned from `void main()`
fix bug in Expression::extractLast
fix use of NrvoWalker

If fbody is the rewritten statement, the replaceCurrent should modify the fbody.
[Refactoring] fbody->semantic() does not modify FuncDeclarataion::type
[Refactoring] CtorDeclaration::syntaxCopy()
fix Issue 13336 - auto ref return deduced to be ref despite return value coercion
+try