Add shared enum types for value type sharing in IL2CPP.

Author: joncham

mcs/class/corlib/LinkerDescriptor/mscorlib.xml

@@ -842,5 +842,16 @@
 		<type fullname="Mono.RuntimeStructs/HandleStackMark" />
 		<!-- marshal.c (mono_marshal_get_native_wrapper) -->
 		<type fullname="Mono.RuntimeStructs/MonoError" />
+
+		<!-- IL2CPP enum sharing -->
+		<type fullname="System.SByteEnum" />
+		<type fullname="System.Int16Enum" />
+		<type fullname="System.Int32Enum" />
+		<type fullname="System.Int64Enum" />
+		
+		<type fullname="System.ByteEnum" />
+		<type fullname="System.UInt16Enum" />
+		<type fullname="System.UInt32Enum" />
+		<type fullname="System.UInt64Enum" />
 	</assembly>
 </linker>

mcs/class/corlib/System/EnumSharing.cs

@@ -0,0 +1,18 @@
+using System;
+
+#if UNITY_AOT
+
+namespace System
+{
+	enum SByteEnum : sbyte {}
+	enum Int16Enum : short {}
+	enum Int32Enum : int {}
+	enum Int64Enum : long {}
+
+	enum ByteEnum : byte {}
+	enum UInt16Enum : ushort {}
+	enum UInt32Enum : uint {}
+	enum UInt64Enum : ulong {}
+}
+
+#endif

mcs/class/corlib/corlib.dll.sources

@@ -104,6 +104,7 @@ System/Delegate.cs
 System/DelegateSerializationHolder.cs
 System/DomainManagerInitializationFlags.cs
 System/EmptyArray.cs
+System/EnumSharing.cs
 System/Environment.cs
 System/EnvironmentVariableTarget.cs
 System/Guid.cs