[MERGE #2162 @leirocks] turning on real writebarrier mode on Linux
[MERGE #2162 @leirocks] turning on real writebarrier mode on Linux

Merge pull request #2162 from leirocks:wbon

previousely I made the change to assume all write barrier pages are dirty, regardless there's missing annotation or not, to make the annotation work easier.

Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore