RFR: 8303489: Add a test to verify classes in vmStruct have unuque vtables [v2]

[Alex Menkov]

> Unique vtables for classes in vmStruct data is a requirement for SA to correctly detect hotspot classes.
> The fix adds test to verify this requirement.
> 
> The test fails as expected on Windows if VM is built without RTTI (see JDK-8302817)

Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:

  addressed feedback

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12820/files
  - new: https://git.openjdk.org/jdk/pull/12820/files/4521c29d..ceac098b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12820&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12820&range=00-01

  Stats: 42 lines in 2 files changed: 9 ins; 14 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/12820.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12820/head:pull/12820

PR: https://git.openjdk.org/jdk/pull/12820