Implement debug info for willset/didset, and teach dispatch to be non-virtual

to didset/will set since we don't drop these in the class vtable.


Swift SVN r13056

lib/IRGen/GenClass.cpp

@@ -1083,7 +1083,7 @@ namespace {
       
       // getters and setters funcdecls will be handled by their parent
       // var/subscript.
-      if (method->isGetterOrSetter()) return;
+      if (method->isAccessor()) return;
       
       llvm::Constant *entry = emitObjCMethodDescriptor(IGM, method);
       if (!method->isStatic()) {