Fix warnings for all fields required/used in the native end

source/System/AppDomain.cs

@@ -15,9 +15,13 @@ namespace System
     /// </summary>
     public sealed class AppDomain : MarshalByRefObject
     {
+        // these fields are required in the native end
+#pragma warning disable 0649, 0169
         [FieldNoReflection]
         private object _appDomain;
         private string _friendlyName;
+#pragma warning restore 0649
+#pragma warning restore 0169
 
         private AppDomain()
         {

source/System/Boolean.cs

@@ -21,7 +21,10 @@ public struct Boolean
         /// </summary>
         public static readonly string TrueString = "True";
 
+        // this field is required in the native end
+#pragma warning disable 0649
         private bool _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Converts the value of this instance to its equivalent string representation (either "True" or "False").

source/System/Byte.cs

@@ -14,7 +14,10 @@ namespace System
     [Serializable]
     public struct Byte
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         private byte _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the largest possible value of a Byte. This field is constant.

source/System/Char.cs

@@ -12,7 +12,10 @@ namespace System
     [Serializable]
     public struct Char
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         private char _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the largest possible value of a Char. This field is constant.

source/System/Double.cs

@@ -15,7 +15,10 @@ namespace System
     [Serializable]
     public struct Double
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         internal double _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the smallest possible value of a Double. This field is constant.

source/System/Exception.cs

@@ -17,7 +17,10 @@ public class Exception
         private readonly string _message;
         private readonly Exception _innerException;
 
+        // this field is required in the native end
+#pragma warning disable 0169
         private object _stackTrace;
+#pragma warning restore 0169
 
         /// <summary>
         /// Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception.

source/System/Int16.cs

@@ -14,7 +14,10 @@ namespace System
     [Serializable]
     public struct Int16
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         internal short _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the largest possible value of an Int16. This field is constant.

source/System/SByte.cs

@@ -14,7 +14,10 @@ namespace System
     [Serializable, CLSCompliant(false)]
     public struct SByte
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         private sbyte _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the largest possible value of SByte. This field is constant.

source/System/Threading/Thread.cs

@@ -14,13 +14,16 @@ namespace System.Threading
     /// </summary>
     public sealed class Thread
     {
+        // these fields are required in the native end
+#pragma warning disable 0169
         private Delegate _delegate;
         private int _priority;
         [Reflection.FieldNoReflection]
         private object _thread;
         [Reflection.FieldNoReflection]
         private object _appDomain;
         private int _id;
+#pragma warning restore 0169
 
         /// <summary>
         /// Initializes a new instance of the Thread class.

source/System/Threading/Timer.cs

@@ -20,10 +20,13 @@ namespace System.Threading
     /// </summary>
     public sealed class Timer : MarshalByRefObject, IDisposable
     {
+        // these fields are required in the native end
+#pragma warning disable 0169
         [Reflection.FieldNoReflection]
         private object _timer;
         private object _state;
         private TimerCallback _callback;
+#pragma warning restore 0169
 
         /// <summary>
         /// Initializes a new instance of the Timer class, using a 32-bit signed integer to specify the time interval.

source/System/UInt16.cs

@@ -14,7 +14,10 @@ namespace System
     [Serializable, CLSCompliant(false)]
     public struct UInt16
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         private ushort _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the largest possible value of UInt16. This field is constant.

source/System/UInt32.cs

@@ -14,7 +14,10 @@ namespace System
     [Serializable, CLSCompliant(false)]
     public struct UInt32
     {
+        // this field is required in the native end
+#pragma warning disable 0649
         private uint _value;
+#pragma warning restore 0649
 
         /// <summary>
         /// Represents the largest possible value of UInt32. This field is constant.