Cache the support dir path.

OpenRA.Game/Platform.cs

@@ -62,9 +62,10 @@ namespace OpenRA
 			}
 		}
 
-		public static string SupportDir
-		{
-			get
+		public static string SupportDir { get { return supportDir.Value; } }
+		static Lazy<string> supportDir = Exts.Lazy(GetSupportDir);
+
+		static string GetSupportDir()
 		{
 			// Use a local directory in the game root if it exists
 			if (Directory.Exists("Support"))
@@ -91,7 +92,6 @@ namespace OpenRA
 
 			return dir + Path.DirectorySeparatorChar;
 		}
-		}
 
 		public static string GameDir { get { return AppDomain.CurrentDomain.BaseDirectory; } }