[8u] RFR (XS) 8231201: hs_err should print coalesced safepoint operations in Events section

[Aleksey Shipilev]

Original fix:
  https://bugs.openjdk.java.net/browse/JDK-8231201
  https://hg.openjdk.java.net/jdk/jdk/rev/4eebb9aadbe3

Patch does not apply to 8u cleanly, because context is a bit different. 8u webrev:
  https://cr.openjdk.java.net/~shade/8231201/webrev.8u.01/

Testing: build; eyeballing hs_errs

-- 
Thanks,
-Aleksey