RFR (S) 8157171: Hook up Unsafe.weakCompareAndSetVolatile to VarHandles

[Aleksey Shipilev]

Hi,

Now that jdk9/hs merged to jdk9/dev, we can finally make a move to
connect new Unsafe.weakCompareAndSetVolatile intrinsics with VarHandles:
  https://bugs.openjdk.java.net/browse/JDK-8157171

Webrev:
  http://cr.openjdk.java.net/~shade/8157171/webrev.01/

The core changes are in the template files, actual .java files were
generated from templates. I also fixed up the few missing VarHandles
tests for weakCASVolatile.

Testing: local Linux x86_64 build; java/lang/invoke/VarHandles jtregs.

Thanks,
-Aleksey