RFR: 8358693: [leyden] Bootstrapping circularity leads to never starting preload threads [v2]

[Aleksey Shipilev]

> This relates to [JDK-8358690](https://bugs.openjdk.org/browse/JDK-8358690), but we want to make sure Leyden preload runs until we have a fuller fix.
> 
> Additional testing:
>  - [x] Ad-hoc perf tests
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`

Aleksey Shipilev 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 three additional commits since the last revision:

 - Move
 - Merge branch 'premain' into JDK-8358693-regression-no-preload
 - Fix

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

Changes:
  - all: https://git.openjdk.org/leyden/pull/75/files
  - new: https://git.openjdk.org/leyden/pull/75/files/d0c8c5c4..baa13edd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=75&range=01
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=75&range=00-01

  Stats: 19 lines in 3 files changed: 8 ins; 9 del; 2 mod
  Patch: https://git.openjdk.org/leyden/pull/75.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/75/head:pull/75

PR: https://git.openjdk.org/leyden/pull/75