RFR: 8349457: [leyden] Workaround Leyden problems with -XX:-TieredCompilation [v4]

[Aleksey Shipilev]

> Currently, supplying `-XX:-TieredCompilation` would break with Leyden workflows, because the archive-backed code cache heap would only be created if `SegmentedCodeCache` is enabled. With default compilation policy, this happens normally when tiered compilation is enabled, but not without it.
> 
> There are other minor peculiarities that we need to handle, which are exposed with `runtime/cds` + `-XX:-TieredCompilation` runs.
> 
> This prevents us from testing C2-only Leyden configs and studying compilation dynamics without tiered policy getting in the way.
> 
> Additional testing:
>  - [x] Ad-hoc Leyden experiments now work with `-XX:-TieredCompilation`: the C2-only code is being stored and loaded successfully from the CDS archive
>  - [x] `runtime/cds` now passes with `-XX:-TieredCompilation`
>  - [x] `runtime/cds` still passes by default (i.e. with tiered compilation)

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 five additional commits since the last revision:

 - Merge branch 'premain' into JDK-8349457-enable-c2
 - Revert Precompiler additions
 - Merge branch 'premain' into JDK-8349457-enable-c2
 - More fixes
 - Fix

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

Changes:
  - all: https://git.openjdk.org/leyden/pull/32/files
  - new: https://git.openjdk.org/leyden/pull/32/files/ee4d9d11..6cdde259

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=32&range=03
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=32&range=02-03

  Stats: 14 lines in 1 file changed: 0 ins; 3 del; 11 mod
  Patch: https://git.openjdk.org/leyden/pull/32.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/32/head:pull/32

PR: https://git.openjdk.org/leyden/pull/32