Ensure that the Aggregate Target doesn't link vendored dependencies

As either the user project or the frameworks are responsible for that aspect and this can cause issues with duplicate symbols.

lib/cocoapods/installer/target_installer/aggregate_target_installer.rb

@@ -32,8 +32,14 @@ module Pod
 
       private
 
+      # Ensure that vendored static frameworks and libraries are not linked
+      # twice to the aggregate target, which shares the xcconfig of the user
+      # target.
+      #
       def custom_build_settings
         settings = {
+          'OTHER_LDFLAGS'      => '',
+          'OTHER_LIBTOOLFLAGS' => '',
           'PODS_ROOT'          => '$(SRCROOT)',
         }
         super.merge(settings)