RFR: 8260301: misc gc/g1/unloading tests fails with "RuntimeException: Method could not be enqueued for compilation at level N"

[Vladimir Kozlov]

On return WB wait to acquire Compile_lock before checking compilation status
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/prims/whitebox.cpp#L988 

This lock is used by ciEnv for compiled code publishing:
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/ci/ciEnv.cpp#L981

So while WB waits the lock compiler thread can finish compilation, register nmethod and clear method's queued_for_compilation bit.

The problem is that WB check `nm` value (compiled code) which it got before the lock and when method compilation is not finished.

The fix is to check compiled code again similar to check in CompileBroker:
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/compiler/compileBroker.cpp#L1501 

Passed hs-tier1-4 testing and 100 x vmTestbase/gc/g1/unloading/tests/unloading_compilation_*.

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Commit messages:
 - 8260301: misc gc/g1/unloading tests fails with "RuntimeException: Method could not be enqueued for compilation at level N"

Changes: https://git.openjdk.java.net/jdk/pull/2356/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2356&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260301
  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2356.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2356/head:pull/2356

PR: https://git.openjdk.java.net/jdk/pull/2356