Add a test that tests re-entrant upcalls, which is a use-case that is uncovered by testing until now.
------------- Commit messages: - add reentrant upcalls test Changes: https://git.openjdk.org/jdk/pull/12927/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12927&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8303001 Stats: 122 lines in 2 files changed: 122 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/12927.diff Fetch: git fetch https://git.openjdk.org/jdk pull/12927/head:pull/12927 PR: https://git.openjdk.org/jdk/pull/12927
