RFR (XS): 8213829: Remove circular dependency between g1CollectedHeap and g1ConcurrentMark

[Kim Barrett]

> On Nov 14, 2018, at 3:33 AM, Man Cao <manc at google.com> wrote:
> 
> Thanks for the review.
> 
> I don't know the internals of GCC well enough to explain this issue, but it is related to function template instantiation due to g1ConcurrentMark.inline.hpp.
> I'm looking at objdump output of g1BarrierSet.cpp in order to diagnose a performance difference between Clang and GCC builds. Once g1ConcurrentMark.inline.hpp gets transitively included, g1BarrierSet.o contains many instantiations of function templates unrelated to the G1BarrierSet class.

Thanks for the additional details.