RFR(XL): 8224675: Late GC barrier insertion for ZGC

[Roland Westrelin]

> http://cr.openjdk.java.net/~neliasso/8224675/webrev.07/

vmSymbols.cpp has no change?

in compile.cpp, indentation looks wrong:

2406     bs->barrier_insertion_phase(C, igvn);
2407     if (failing())  return;

That looks good to me. No need for another webrev.

Roland.