title: UIToolbar with UIBarButtonItem LayoutConstraint issue
body: <p>I'm creating a UIToolbar with UIBarButtonItem in it programatically. I'm not using .xib or storyboard for this ViewController. Here's the code of how I created it. </p>
  
  <pre><code>NSMutableArray *items = [[NSMutableArray alloc] init];
  
  UIBarButtonItem *buttonItem;
  buttonItem = [[UIBarButtonItem alloc ] initWithTitle: [Language get:@"Home" alter:nil]
                                                 style: UIBarButtonItemStyleBordered
                                                target: self
                                                action: @selector(viewChangeTo)];
  [items addObject:buttonItem];
  
  toolbar = [[UIToolbar alloc] init];
  toolbar.frame = CGRectMake(0, 0, 1024, 44);
  [toolbar setItems:items animated:NO];
  [self.view addSubview:toolbar];
  </code></pre>
  
  <p>Each time the view get loaded I'm getting the LayoutConstraints error. </p>
  
  <pre><code>[LayoutConstraints] Unable to simultaneously satisfy constraints.
  Probably at least one of the constraints in the following list is one you don't want. 
  Try this: 
      (1) look at each constraint and try to figure out which you don't expect; 
      (2) find the code that added the unwanted constraint or constraints and fix it. 
  
  "&lt;NSLayoutConstraint:0x6000023de350 H:|-(20)-[_UIModernBarButton:0x7fed8c463e00'Home']   (active, names: '|':_UIButtonBarButton:0x7fed8c463bb0 )&gt;",
  "&lt;NSLayoutConstraint:0x6000023de3a0 H:[_UIModernBarButton:0x7fed8c463e00'Home']-(20)-|   (active, names: '|':_UIButtonBarButton:0x7fed8c463bb0 )&gt;",
  "&lt;NSLayoutConstraint:0x6000023dff70 '_UITemporaryLayoutWidth' _UIButtonBarButton:0x7fed8c463bb0.width == 0   (active)&gt;
  
  Will attempt to recover by breaking constraint 
  </code></pre>
  
  <p></p>
  
  <pre><code>Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
  The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in &lt;UIKitCore/UIView.h&gt; may also be helpful.
  2019-01-21 13:14:24.777354+0800 M[50994:10130357] [LayoutConstraints] Unable to simultaneously satisfy constraints.
      Probably at least one of the constraints in the following list is one you don't want. 
      Try this: 
          (1) look at each constraint and try to figure out which you don't expect; 
          (2) find the code that added the unwanted constraint or constraints and fix it. 
  (
      "&lt;NSLayoutConstraint:0x6000023de530 _UIModernBarButton:0x7fed8c463e00'Home'.lastBaseline == UILayoutGuide:0x6000039eef40'UIViewLayoutMarginsGuide'.bottom   (active)&gt;",
      "&lt;NSLayoutConstraint:0x6000023de580 V:|-(&gt;=0)-[_UIModernBarButton:0x7fed8c463e00'Home']   (active, names: '|':_UIButtonBarButton:0x7fed8c463bb0 )&gt;",
      "&lt;NSLayoutConstraint:0x6000023e5680 UIButtonLabel:0x7fed8c457e90'Home'.centerY == _UIModernBarButton:0x7fed8c463e00'Home'.centerY + 1.5   (active)&gt;",
      "&lt;NSLayoutConstraint:0x6000023e4c80 '_UITemporaryLayoutHeight' _UIButtonBarButton:0x7fed8c463bb0.height == 0   (active)&gt;",
      "&lt;NSLayoutConstraint:0x6000023de490 'UIView-bottomMargin-guide-constraint' V:[UILayoutGuide:0x6000039eef40'UIViewLayoutMarginsGuide']-(16)-|   (active, names: '|':_UIButtonBarButton:0x7fed8c463bb0 )&gt;"
  )
  
  Will attempt to recover by breaking constraint 
  &lt;NSLayoutConstraint:0x6000023e5680 UIButtonLabel:0x7fed8c457e90'Home'.centerY == _UIModernBarButton:0x7fed8c463e00'Home'.centerY + 1.5   (active)&gt;
  
  Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
  The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in &lt;UIKitCore/UIView.h&gt; may also be helpful.
  </code></pre>