move Unsafe.get{Object|Int}Volatile from classpath-openjdk.cpp to builtin.cpp

This makes them available in all class libraries, not just the OpenJDK
library.  Note that I've also removed the unecessary idle statements,
per ab4adef.
Merge pull request #188 from dicej/volatile

move Unsafe.get{Object|Int}Volatile from classpath-openjdk.cpp to builti...