RFR 8225374 [lworld][c1] TestMethodHandles.java fails with -XX:+StressValueTypeReturnedAsFields

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8225374
http://cr.openjdk.java.net/~iklam/valhalla/8225374-TestMethodHandles-fails-with-StressValueTypeReturnedAsFields.v01/

Summary:

When a C1-compiled method calls a method handle invoker, it needs to 
check if the
returned oop value indicates that the fields of the oop have been returned
in registers (lowest bit of the returned "oop" is 1). If so, pack the fields
back into a buffered object.

Thanks
- Ioi