Fixed a large number of build warnings

Source/OpenTK/INativeWindow.cs

@@ -261,12 +261,12 @@ namespace OpenTK
         event EventHandler<EventArgs> MouseEnter;
 
         /// <summary>
-        /// Occurs whenever a <see cref="MouseButton"/> is clicked.
+        /// Occurs whenever a <see cref="OpenTK.Input.MouseButton"/> is clicked.
         /// </summary>
         event EventHandler<Input.MouseButtonEventArgs> MouseDown;
 
         /// <summary>
-        /// Occurs whenever a <see cref="MouseButton"/> is released.
+        /// Occurs whenever a <see cref="OpenTK.Input.MouseButton"/> is released.
         /// </summary>
         event EventHandler<Input.MouseButtonEventArgs> MouseUp;
 

Source/OpenTK/Platform/Linux/Bindings/Drm.cs

@@ -30,6 +30,8 @@
 using System;
 using System.Runtime.InteropServices;
 
+#pragma warning disable 0649 // field is never assigned
+
 namespace OpenTK.Platform.Linux
 {
     [UnmanagedFunctionPointer(CallingConvention.Cdecl)]

Source/OpenTK/Platform/Linux/Bindings/Libc.cs

@@ -31,6 +31,8 @@ using System;
 using System.Runtime.InteropServices;
 using System.Text;
 
+#pragma warning disable 0649 // field is never assigned
+
 namespace OpenTK.Platform.Linux
 {
     partial class Libc

Source/OpenTK/Platform/Windows/XInputJoystick.cs

@@ -237,6 +237,8 @@ namespace OpenTK.Platform.Windows
             Any = 0xff
         }
 
+#pragma warning disable 0649 // field is never assigned
+
         struct XInputThresholds
         {
             public const int LeftThumbDeadzone = 7849;