Unique the list of vendored frameworks.

Since those are full paths, uniquing the list ensures we only consider
each framework once for the check, no matter if it is linked against
multiple targets.

lib/cocoapods/installer.rb

@@ -390,7 +390,7 @@ module Pod
       aggregate_targets.each do |aggregate_target|
         aggregate_target.user_build_configurations.keys.each do |config|
           pod_targets = aggregate_target.pod_targets_for_build_configuration(config)
-          vendored_frameworks = pod_targets.flat_map(&:file_accessors).flat_map(&:vendored_frameworks)
+          vendored_frameworks = pod_targets.flat_map(&:file_accessors).flat_map(&:vendored_frameworks).uniq
           frameworks = vendored_frameworks.map { |fw| fw.basename('.framework') }
           frameworks += pod_targets.select { |pt| pt.should_build? && pt.requires_frameworks? }.map(&:product_module_name)