Don't generate Objective C WKT for conformance tests to avoid dupliate defs.

conformance/Makefile.am

 ## Process this file with automake to produce Makefile.in
 
-protoc_inputs =                                                \
-  conformance.proto                                            \
+conformance_protoc_inputs =                                    \
+  conformance.proto
+
+well_known_type_protoc_inputs =                                \
   $(top_srcdir)/src/google/protobuf/any.proto                  \
   $(top_srcdir)/src/google/protobuf/duration.proto             \
   $(top_srcdir)/src/google/protobuf/field_mask.proto           \
@@ -82,8 +84,10 @@ endif
 
 if USE_EXTERNAL_PROTOC
 
-protoc_middleman: $(protoc_inputs)
-	$(PROTOC) -I$(srcdir) -I$(top_srcdir) --cpp_out=. --java_out=. --ruby_out=. --objc_out=. --python_out=.$^
+# Some implementations include pre-generated versions of well-known types.
+protoc_middleman: $(conformance_protoc_inputs) $(well_known_type_protoc_inputs)
+	$(PROTOC) -I$(srcdir) -I$(top_srcdir) --cpp_out=. --java_out=. --ruby_out=. --objc_out=. --python_out=. $(conformance_protoc_inputs)
+	$(PROTOC) -I$(srcdir) -I$(top_srcdir) --cpp_out=. --java_out=. --ruby_out=. --python_out=. $(well_known_type_protoc_inputs)
 	touch protoc_middleman
 
 else
@@ -91,8 +95,9 @@ else
 # We have to cd to $(srcdir) before executing protoc because $(protoc_inputs) is
 # relative to srcdir, which may not be the same as the current directory when
 # building out-of-tree.
-protoc_middleman: $(top_srcdir)/src/protoc$(EXEEXT) $(protoc_inputs)
-	oldpwd=`pwd` && ( cd $(srcdir) && $$oldpwd/../src/protoc$(EXEEXT) -I. -I$(top_srcdir)/src --cpp_out=$$oldpwd --java_out=$$oldpwd --ruby_out=$$oldpwd --objc_out=$$oldpwd --python_out=$$oldpwd $(protoc_inputs) )
+protoc_middleman: $(top_srcdir)/src/protoc$(EXEEXT) $(conformance_protoc_inputs) $(well_known_type_protoc_inputs)
+	oldpwd=`pwd` && ( cd $(srcdir) && $$oldpwd/../src/protoc$(EXEEXT) -I. -I$(top_srcdir)/src --cpp_out=$$oldpwd --java_out=$$oldpwd --ruby_out=$$oldpwd --objc_out=$$oldpwd --python_out=$$oldpwd $(conformance_protoc_inputs) )
+	oldpwd=`pwd` && ( cd $(srcdir) && $$oldpwd/../src/protoc$(EXEEXT) -I. -I$(top_srcdir)/src --cpp_out=$$oldpwd --java_out=$$oldpwd --ruby_out=$$oldpwd --python_out=$$oldpwd $(well_known_type_protoc_inputs) )
 	touch protoc_middleman
 
 endif