destructors: some improvements for bug #4214: object constructors are moved too

tests/destructor/tmove_objconstr.nim

@@ -0,0 +1,32 @@
+
+discard """
+output:  '''test created
+test destroyed 0'''
+  cmd: '''nim c --newruntime $file'''
+"""
+
+# bug #4214
+type
+  Data = object
+    data: string
+    rc: int
+
+proc `=destroy`(d: var Data) =
+  dec d.rc
+  echo d.data, " destroyed ", d.rc
+
+proc `=`(dst: var Data, src: Data) =
+  echo src.data, " copied"
+  dst.data = src.data & " (copy)"
+  dec dst.rc
+  inc dst.rc
+
+proc initData(s: string): Data =
+  result = Data(data: s, rc: 1)
+  echo s, " created"
+
+proc main =
+  var x = initData"test"
+
+when isMainModule:
+  main()