RFR: ZGC: C2: Fix and enable clone intrinsic

[Roland Westrelin]

Hi Nils,

> Webrev: http://cr.openjdk.java.net/~neliasso/zgc/fix_clone/webrev/

I'm surprised that works. kit.access_load_at() needs, at least, a memory
state that it should get from kit but kit is:

GraphKit kit;

current memory state is not passed to the GraphKit constructor so
GraphKit can't have the right memory state.

You could use the other constructor GraphKit::GraphKit(JVMState* jvms)
and use the jvms from the ArrayCopyNode but I think that would break if
this code is called from an igvn.

Roland.