[master] RFR: 8301562: [Lilliput] Runtime flag to enable Lilliput [v2]

[Roman Kennke]

> This change introduces an experimental runtime flag -XX:[+/-]UseCompactObjectHeaders which can be used to disable Lilliput. The flag guards all the relevant places that directly affect the object layout and the accesses to Klass* etc. The change also restores the previous behaviour when -UseCompactObjectHeaders is selected.
> 
> Testing:
>  - [x] tier1 (x86_64, x86_32, aarch64) +UseCompactObjectHeaders
>  - [x] tier2 (x86_64, x86_32, aarch64) +UseCompactObjectHeaders
>  - [x] tier1 (x86_64, x86_32, aarch64) -UseCompactObjectHeaders
>  - [x] tier2 (x86_64, x86_32, aarch64) -UseCompactObjectHeaders

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Fix tests for 32bit builds

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

Changes:
  - all: https://git.openjdk.org/lilliput/pull/70/files
  - new: https://git.openjdk.org/lilliput/pull/70/files/becf81c0..d32fc54c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=lilliput&pr=70&range=01
 - incr: https://webrevs.openjdk.org/?repo=lilliput&pr=70&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/lilliput/pull/70.diff
  Fetch: git fetch https://git.openjdk.org/lilliput pull/70/head:pull/70

PR: https://git.openjdk.org/lilliput/pull/70