for review: 8236522: "always atomic" modifier for inline classes to enforce atomicity

[John Rose]

Define a new modifier which enforces atomicity of all instances (in the heap) of the given inline class. 

Working title "__AlwaysAtomic". Suggested final "alwaysatomic" or just "atomic". 

Represented in classfile using currently free modifier bit 0x0040 = ACC_VOLATILE.

https://bugs.openjdk.java.net/browse/JDK-8236522
http://cr.openjdk.java.net/~jrose/jvm/atomic-8236522