Enabled users to remove any built-in pass. (#829)

Fixes https://github.com/mono/CppSharp/issues/802

src/Generator/Driver.cs

@@ -497,9 +497,11 @@ namespace CppSharp
             if (!options.Quiet)
                 Diagnostics.Message("Processing code...");
 
+            driver.SetupPasses(library);
+
             library.Preprocess(driver, driver.Context.ASTContext);
 
-            driver.SetupPasses(library);
+
 
             driver.ProcessCode();
             library.Postprocess(driver, driver.Context.ASTContext);