Marked Array.Empty FailsOnMono, as it comes only in 4.6 API.

Author: iskiselev

Tests/SimpleTestCases/ArrayEmpty.cs …impleTestCases/FailsOnMono/ArrayEmpty.csTests/SimpleTestCases/ArrayEmpty.cs renamed to Tests/SimpleTestCases/FailsOnMono/ArrayEmpty.cs Tests/SimpleTestCases/ArrayEmpty.cs renamed to Tests/SimpleTestCases/FailsOnMono/ArrayEmpty.cs

@@ -134,7 +134,7 @@
     <None Include="SimpleTestCases\ReflectionPositionalGenericNames_Issue509.cs" />
     <None Include="SimpleTestCases\ArrayType.cs" />
     <None Include="SimpleTestCases\Issue844.cs" />
-    <None Include="SimpleTestCases\ArrayEmpty.cs" />
+    <None Include="SimpleTestCases\FailsOnMono\ArrayEmpty.cs" />
     <Compile Include="SimpleTests.cs" />
     <None Include="SimpleTestCases\BaseAutoProperties.cs" />
     <None Include="SimpleTestCases\OverloadedVirtualMethods.cs" />