[XCConfigHelper] Fix the `OTHER_SWIFT_FLAGS` generated, so `#if COCOAPODS` works in Swift.

Closes https://github.com/CocoaPods/CocoaPods/issues/2983.

CHANGELOG.md

@@ -35,6 +35,10 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   [Samuel Giddins](https://github.com/segiddins)
   [#3137](https://github.com/CocoaPods/CocoaPods/issues/3137)
 
+* Fix the `OTHER_SWIFT_FLAGS` generated, so `#if COCOAPODS` works in Swift.  
+  [Samuel Giddins](https://github.com/segiddins)
+  [#2983](https://github.com/CocoaPods/CocoaPods/issues/2983)
+
 
 ## 0.36.0.beta.2
 

lib/cocoapods/generator/xcconfig/xcconfig_helper.rb

@@ -160,7 +160,7 @@ module Pod
         def self.add_language_specific_settings(target, xcconfig)
           if target.uses_swift?
             build_settings = {
-              'OTHER_SWIFT_FLAGS' => quote(['-D COCOAPODS']),
+              'OTHER_SWIFT_FLAGS' => quote(%w(-D COCOAPODS)),
             }
             xcconfig.merge!(build_settings)
           end

spec/unit/generator/xcconfig/aggregate_xcconfig_spec.rb

@@ -143,7 +143,7 @@ module Pod
           end
 
           it 'adds the COCOAPODS macro definition' do
-            @xcconfig.to_hash['OTHER_SWIFT_FLAGS'].should.include '-D COCOAPODS'
+            @xcconfig.to_hash['OTHER_SWIFT_FLAGS'].should.include '"-D" "COCOAPODS"'
           end
         end