Added platform specific DefineConstants for RELEASE configuration for MonoGame IOS

spine-monogame/xamarinstudio-ios/src/spine-monogame-xamarinstudio-ios.csproj

@@ -29,6 +29,7 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <ConsolePause>false</ConsolePause>
+    <DefineConstants>IOS</DefineConstants>
   </PropertyGroup>
   <ItemGroup>
     <Reference Include="System" />