RFR: 8187809: UseMembar should be set true and deprecate the flag

[Robbin Ehn]

Hi all, please review!

This patch set the default technique for reading thread state to memory barriers instead of using the asymmetric dekker 
synchronization on all platforms. We also deprecate the option and starting the removal process. There have been 
discussion with people involved in all platforms and we will have another discussion before obsoleting the flag to make 
sure no issue have been found.

More info in CSR:
https://bugs.openjdk.java.net/browse/JDK-8187812

Bug:
https://bugs.openjdk.java.net/browse/JDK-8187809

Code:
http://cr.openjdk.java.net/~rehn/8187809/webrev/

Thanks, Robbin