Added missing Platform class file.

src/Core/Platform.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace CppSharp
+{
+    public static class Platform
+    {
+        public static bool IsWindows
+        {
+            get
+            {
+                switch (Environment.OSVersion.Platform)
+                {
+                    case PlatformID.Win32NT:
+                    case PlatformID.Win32S:
+                    case PlatformID.Win32Windows:
+                    case PlatformID.WinCE:
+                        return true;
+                }
+
+                return false;
+            }
+        }
+
+        [DllImport("libc")]
+        static extern int uname(IntPtr buf);
+
+        public static bool IsMacOS
+        {
+            get
+            {
+                if (Environment.OSVersion.Platform != PlatformID.Unix)
+                    return false;
+
+                IntPtr buf = Marshal.AllocHGlobal(8192);
+                if (uname(buf) == 0)
+                {
+                    string os = Marshal.PtrToStringAnsi(buf);
+                    switch (os)
+                    {
+                        case "Darwin":
+                            return true;
+                    }
+                }
+                Marshal.FreeHGlobal(buf);
+
+                return false;
+            }
+        }
+}