RFR: Merge upstream C1 modularization

[Roman Kennke]

This is a big but important one. The change merges upstream's C1
modularization and adopts Shenandoah C1 barriers to it.

It gets rid of most/all changes in c1_LIRGenerator and related code. It
also moves the cmpxchg assembly from MacroAssembler to
BarrierSetAssembler. Overall this means a very significant reduction in
shared code changes against upstream.

Testing: hotspot_gc_shenandoah (release/fastdebug), specjvm with
different heuristics (adaptive,traversal,connected)

This patch does not do the necessary changes for AArch64, this will be
broken until I get to fix it. It'll be the very next thing on my list.
(I don't know how to easily transfer the change+merge changes over to
the aarch64 box - without syncing the complete workspace - to make it a
single push).

http://cr.openjdk.java.net/~rkennke/upstream-merge-2018-06-02/webrev.00/

Ok?