RFR(XS): 8218468: Load barrier slow path node should be MachTypeNode

[Nils Eliasson]

Hi,

We have a number of assert failures in RunThese testing. This is caused 
by  LoadBarrierSlowReg and LoadBarrierWeakSlowReg not being MachTypeNodes.

This patches fixes that.

I am also adding includes for ZGC and Shenandoah.

Bug: https://bugs.openjdk.java.net/browse/JDK-8218468

Webrev: http://cr.openjdk.java.net/~neliasso/8218468/webrev.01/

Please review,

Nils Eliasson