[8u] RFR: 8146612: C2: Precedence edges specification violated

[Roland Westrelin]

Change does not apply cleanly to 8u in node.hpp (copyright change) and
node.cpp: (copyright change and methods
Node::del_req()/Node::del_req_ordered()). The 8u change is identical to
the one from 11u but code in Node::del_req()/Node::del_req_ordered()
changed abit. This is required in order to backport 8214862: assert(proj
!= __null) at compile.cpp:3251.

http://cr.openjdk.java.net/~roland/8146612.8u/webrev.00/

Initial change:
https://bugs.openjdk.java.net/browse/JDK-8146612
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/f6615ec051d9

Tested with tier1.

Roland.