RFR (S): CR 8004318/JEP 171 Fences intrinsics

[Aleksey Shipilev]

(submitting this on behalf of Doug Lea)

Hi,

Please see the preliminary webrev for changes associated with JEP 171
aka Fences [1]. The webrev is here:
  http://shipilev.net/pub/jdk/hotspot/fences/webrev-1/

Testing:
 - built and tested on Linux x86_64
 - java-concurrency-torture [2] fences tests [3] passes on Linux x86_64
 - looking through generated assembly for torture tests

Please review the code changes while this thing flies through JPRT and
JEP is being "funded".

Thanks,
Aleksey.

[1] http://openjdk.java.net/jeps/171
[2] https://github.com/shipilev/java-concurrency-torture
[3] java -jar concurrency-torture.jar -t ".*fences.*"