[PodTargetSettings] Say there is no module map to import when the target is not being built

lib/cocoapods/target/build_settings.rb

@@ -650,6 +650,7 @@ module Pod
 
         # @return [Array<String>]
         define_build_settings_method :module_map_file_to_import, :memoized => true do
+          return unless target.should_build?
           return if target.requires_frameworks?
           return unless target.defines_module?
 

spec/unit/target/build_settings/pod_target_settings_spec.rb

@@ -176,6 +176,12 @@ module Pod
             @xcconfig.to_hash['PRODUCT_BUNDLE_IDENTIFIER'].should == 'org.cocoapods.${PRODUCT_NAME:rfc1034identifier}'
           end
 
+          it 'does not have a module map to import if it is not built' do
+            @pod_target.stubs(:should_build? => false, :requires_frameworks? => false, :defines_module? => true)
+            @generator.generate
+            @generator.module_map_file_to_import.should.be.nil
+          end
+
           it 'saves the xcconfig' do
             path = temporary_directory + 'sample.xcconfig'
             @generator.save_as(path)