Make the FNF exception light up more robust

src/Compilers/Shared/DesktopShim.cs

@@ -14,12 +14,11 @@ internal static class DesktopShim
     {
         internal static class FileNotFoundException
         {
-            internal static readonly Type Type = ReflectionUtilities.TryGetType(
-               "System.IO.FileNotFoundException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a");
+            internal static readonly Type Type = typeof(FileNotFoundException);
 
             private static PropertyInfo s_fusionLog = Type?.GetTypeInfo().GetDeclaredProperty("FusionLog");
 
-            internal static string TryGetFusionLog(object obj) => s_fusionLog.GetValue(obj) as string;
+            internal static string TryGetFusionLog(object obj) => s_fusionLog?.GetValue(obj) as string;
         }
     }
 }