[master] RFR: Preserve Klass* in leak profiler [v4]

[Roman Kennke]

> The JFR leak profiler uses the mark word for marking objects during traversal, and for storing pointers to Edges. We need to preserve the compressed Klass* in the upper part of the mark-word during the traversal.
> 
> The change is based on: openjdk/jdk/pull/5918
> 
> Testing:
>  - [x] jdk/jfr (x86_64)
>  - [x] jdk/jfr (x86_32)
>  - [x] tier1
>  - [x] tier2

Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:

 - Merge branch 'master' into fix-jfr-2
 - Merge branch 'master' into fix-jfr-2
 - Cherry-pick  8275277: assert(dest_attr.is_in_cset() == (obj->forwardee() == obj)) failed
 - Merge branch 'master' into fix-jfr-2
 - Merge branch 'pull/5918' into fix-jfr-2
 - remove -1
 - constants
 - Fix 32bit build
 - Merge branch 'master' into fix-jfr-2
 - In leakprofiler, don't override Klass when marking objects
 - ... and 3 more: https://git.openjdk.java.net/lilliput/compare/eeef004d...bf8aa74a

-------------

Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/21/files
  - new: https://git.openjdk.java.net/lilliput/pull/21/files/029c37a1..bf8aa74a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=21&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=21&range=02-03

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/21.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/21/head:pull/21

PR: https://git.openjdk.java.net/lilliput/pull/21