c_message.cc: Resolve name conflict (Fixes #389)

protoc-c/c_message.cc

@@ -169,7 +169,7 @@ GenerateStructDefinition(io::Printer* printer) {
       }
       printer->Print(vars, "$ucclassname$__$oneofname$_$fieldname$ = $fieldnum$$opt_comma$\n");
     }
-    printer->Print(vars, "  PROTOBUF_C__FORCE_ENUM_TO_BE_INT_SIZE($ucclassname$__$oneofname$)\n");
+    printer->Print(vars, "  PROTOBUF_C__FORCE_ENUM_TO_BE_INT_SIZE($ucclassname$__$oneofname$__CASE)\n");
     printer->Outdent();
     printer->Print(vars, "} $foneofname$Case;\n\n");
   }

t/issue220/issue220.c

@@ -8,6 +8,6 @@ int main(void)
 {
 	assert(_MESSAGE_TYPE1__FLAG_IS_INT_SIZE == INT_MAX);
 	assert(_MESSAGE_TYPE2__ANOTHER_FLAG_IS_INT_SIZE == INT_MAX);
-	assert(_TOP_LEVEL__SUBMESSAGES_IS_INT_SIZE == INT_MAX);
+	assert(_TOP_LEVEL__SUBMESSAGES__CASE_IS_INT_SIZE == INT_MAX);
 	return EXIT_SUCCESS;
 }