Use base_configuration_reference.real_path rather than path (#4118)

real_path has the correct value after a pod deintegrate, while path has
some nearly correct value. No idea why these are different.

Author: wilhuff

scripts/sync_project.rb

@@ -546,7 +546,7 @@ def sync_xcconfig(target_def, target)
         next
       end
 
-      path = PODFILE_DIR.join(config.base_configuration_reference.path)
+      path = PODFILE_DIR.join(config.base_configuration_reference.real_path)
       if !File.file?(path)
         puts "Skipping #{target.name} (#{config.name}); missing xcconfig"
         next