Volatile lazy vals kill vm

[DarkDimius]

https://bugs.openjdk.java.net/browse/JDK-8068239

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x000000010af04691, pid=48994, tid=4867
#
# JRE version: Java(TM) SE Runtime Environment (8.0_25-b17) (build 1.8.0_25-b17)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.25-b02 mixed mode bsd-amd64 compressed oops)
# Problematic frame:
# V  [libjvm.dylib+0x504691]  ObjectSynchronizer::FastHashCode(Thread*, oopDesc*)+0x1bd

Workaround - remove call to identityHashCode from https://github.com/lampepfl/dotty/blob/master/src/dotty/runtime/LazyVals.scala#L80
Unfortunately this makes initializations of same field across all class instances use same monitor for notifications. This is not a very big issue, as synchronization is used only to notify other threads. We do not run any user-defined code in synchronized block.