[system] Small optimization for Xamarin.Mac (where we know we're executing on a Mac)

diff --git a/mcs/class/System/System/Platform.cs b/mcs/class/System/System/Platform.cs
index 8f6f496e906e8fd8cc9dcbbf549e1aebd3065e23..c45a33e66005cff43b6a826cd74b85c3c8c77128 100644 (file)
--- a/mcs/class/System/System/Platform.cs
+++ b/mcs/class/System/System/Platform.cs
@@ -28,7 +28,7 @@ using System.Runtime.InteropServices;
 
 namespace System {
        internal static class Platform {
-#if MONOTOUCH
+#if MONOTOUCH || XAMMAC
                public static bool IsMacOS {
                        get { return true; }
                }