RFR: 8362534: [Leyden] assert(comp != nullptr) failed: Ensure we have a compiler

[Ashutosh Mehra]

Precompiler tries to compile methods at all levels without taking into account TieredStopAtLevel value.
This patch updates Precompiler to restrict compilation to only levels allowed by TieredStopAtLevel.

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Commit messages:
 - 8362534: [Leyden] assert(comp != nullptr) failed: Ensure we have a compiler

Changes: https://git.openjdk.org/leyden/pull/85/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=85&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8362534
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/leyden/pull/85.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/85/head:pull/85

PR: https://git.openjdk.org/leyden/pull/85