Library support for generating BSM for value type's hashCode/equals/toString

[mandy chung]

This is an initial library support to generate BSM for hashCode/equals
/toString for value types.  It implements the idea John laid out [1].
Srikanth will be adding javac support.  Once hook up, we can do more
interesting experiment and improvement and tease out issues.

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/value-hashcode-bsm.00/

Mandy
[1] 
http://mail.openjdk.java.net/pipermail/valhalla-dev/2018-April/004111.html