[crac] RFR: Use special class for exception aggregates [v7]

[Radim Vansa]

> Extracted non-essential changes from other PR.

Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:

  Moved exception after native failure

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

Changes:
  - all: https://git.openjdk.org/crac/pull/64/files
  - new: https://git.openjdk.org/crac/pull/64/files/128b64a3..50926f02

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=64&range=06
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=64&range=05-06

  Stats: 10 lines in 1 file changed: 5 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/crac/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/64/head:pull/64

PR: https://git.openjdk.org/crac/pull/64