Fix Protobuf.podspec

Protobuf.podspec

@@ -11,11 +11,25 @@ Pod::Spec.new do |s|
   s.license  = 'New BSD'
   s.authors  = { 'The Protocol Buffers contributors' => 'protobuf@googlegroups.com' }
 
-  s.source_files = 'objectivec/GPBProtocolBuffers.{h,m}'
-  # GPBProtocolBuffers.{h,m} are umbrella files. We need Cocoapods to preserve the files imported by
-  # them.
-  s.preserve_paths = 'objectivec/*.{h,m}',
-                     'objectivec/google/protobuf/*.pbobjc.{h,m}'
+  s.source_files = 'objectivec/*.{h,m}',
+                   'objectivec/google/protobuf/Any.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/Api.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/Descriptor.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/Duration.pbobjc.h',
+                   'objectivec/google/protobuf/Empty.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/FieldMask.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/SourceContext.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/Struct.pbobjc.{h,m}',
+                   'objectivec/google/protobuf/Timestamp.pbobjc.h',
+                   'objectivec/google/protobuf/Type.pbobjc.{h,m}'
+                   'objectivec/google/protobuf/Wrappers.pbobjc.{h,m}'
+  # Timestamp.pbobjc.m and Duration.pbobjc.m are #imported by GPBWellKnownTypes.m. So we can't
+  # compile them (duplicate symbols), but we need them available for the importing:
+  s.preserve_paths = 'objectivec/google/protobuf/Duration.pbobjc.m',
+                     'objectivec/google/protobuf/Timestamp.pbobjc.m'
+  # The following would cause duplicate symbol definitions. GPBProtocolBuffers is expected to be
+  # left out, as it's an umbrella implementation file.
+  s.exclude_files = 'objectivec/GPBProtocolBuffers.m'
   s.header_mappings_dir = 'objectivec'
 
   s.ios.deployment_target = '7.1'