Fix compile errors.

src/libraries/System.Drawing.Common/src/System/Drawing/Imaging/BitmapData.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace System.Drawing.Imaging

src/libraries/System.Drawing.Common/src/System/Drawing/Pen.cs

@@ -52,7 +52,7 @@ public Pen(Color color, float width)
         {
             _color = color;
 
-            IntPtr pen = IntPtr.Zero;
+            IntPtr pen;
             int status = Gdip.GdipCreatePen1(color.ToArgb(),
                                                 width,
                                                 (int)GraphicsUnit.World,

src/libraries/System.Drawing.Common/src/System/Drawing/SolidBrush.cs

@@ -18,7 +18,7 @@ public SolidBrush(Color color)
         {
             _color = color;
 
-            IntPtr nativeBrush = IntPtr.Zero;
+            IntPtr nativeBrush;
             int status = Gdip.GdipCreateSolidFill(_color.ToArgb(), out nativeBrush);
             Gdip.CheckStatus(status);