Fix #2407: Operator '-' cannot be applied to operand of type 'nuint'

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NativeInts.cs

@@ -200,5 +200,10 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			intptr = intPtr;
 			i = num + 1;
 		}
+
+		public nint NegateUnsigned(nuint x)
+		{
+			return (nint)(0 - x);
+		}
 	}
 }

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1526,9 +1526,9 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				IType rightUType = NullableType.GetUnderlyingType(right.Type);
 				if (rightUType.IsKnownType(KnownTypeCode.Int32) || rightUType.IsKnownType(KnownTypeCode.Int64)
-					|| rightUType.IsCSharpSmallIntegerType() || rightUType.IsCSharpNativeIntegerType())
+					|| rightUType.IsCSharpSmallIntegerType() || rightUType.Kind == TypeKind.NInt)
 				{
-					// unary minus is supported on signed int and long, and on the small integer types (since they promote to int)
+					// unary minus is supported on signed int, nint and long, and on the small integer types (since they promote to int)
 					var uoe = new UnaryOperatorExpression(UnaryOperatorType.Minus, right.Expression);
 					uoe.AddAnnotation(inst.CheckForOverflow ? AddCheckedBlocks.CheckedAnnotation : AddCheckedBlocks.UncheckedAnnotation);
 					var resultType = FindArithmeticType(inst.RightInputType, Sign.Signed);