Trim imports for bundled generated protos.

To avoid a cycle between headers, have the WKTs use minimal imports instead
of using the helper to get everything from the library.

Fixes https://github.com/google/protobuf/issues/4301
Fixes https://github.com/google/protobuf/issues/4403
diff --git a/objectivec/GPBProtocolBuffers_RuntimeSupport.h b/objectivec/GPBProtocolBuffers_RuntimeSupport.h
index fea75b9..04dde62 100644
--- a/objectivec/GPBProtocolBuffers_RuntimeSupport.h
+++ b/objectivec/GPBProtocolBuffers_RuntimeSupport.h
@@ -31,7 +31,7 @@
 // This header is meant to only be used by the generated source, it should not
 // be included in code using protocol buffers.
 
-#import "GPBProtocolBuffers.h"
+#import "GPBBootstrap.h"
 
 #import "GPBDescriptor_PackagePrivate.h"
 #import "GPBExtensionInternals.h"