“Allow non-modular includes in framework modules”

It’s the magic sentence that allows pods dependent on RxLibrary to be
archived correctly by XCode.

It’s less than ideal, and seems arbitrary (why RxLibrary specifically?),
so we’ll try to produce a minimal case and open an issue with it in the
Cocoapods repo.
diff --git a/gRPC-ProtoRPC.podspec b/gRPC-ProtoRPC.podspec
index 9cc33c7..62c9a23 100644
--- a/gRPC-ProtoRPC.podspec
+++ b/gRPC-ProtoRPC.podspec
@@ -62,8 +62,10 @@
   s.dependency 'gRPC', version
   s.dependency 'gRPC-RxLibrary', version
   s.dependency 'Protobuf', '~> 3.0.0-beta-3.1'
-  # This is needed by all pods that depend on Protobuf:
   s.pod_target_xcconfig = {
+    # This is needed by all pods that depend on Protobuf:
     'GCC_PREPROCESSOR_DEFINITIONS' => '$(inherited) GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1',
+    # This is needed by all pods that depend on gRPC-RxLibrary:
+    'CLANG_ALLOW_NON_MODULAR_INCLUDES_IN_FRAMEWORK_MODULES' => 'YES',
   }
 end