Request for reviews (S): 6880053 backport to HS16

[Vladimir Kozlov]

This is backport of the fix in HS17.

http://cr.openjdk.java.net/~kvn/6880053_hs16/webrev.00

Fixed 6880053: assert(alloc_obj->as_CheckCastPP()->type() != TypeInstPtr::NOTNULL)

Problem:
Nightly testing found a case when the type
of the cloned object is TypeInstPtr::NOTNULL
the same as tyoe of second CheckCastPP node in clone()
intrinsic and arraycopy. It produces incorrect graph.

Solution:
Removed second CheckCastPP and instead use MembarCPUOrder
to not let reads from the cloned object float above the arraycopy.

Reviewed by:

Fix verified (y/n): y, test

Other testing:
JPRT