RFR: 8358821: patch_verified_entry causes problems, use nmethod entry barriers instead

[Dean Long]

This PR removes patching of the verified entry point and related code, and replaces it by refactoring the existing nmethod entry barrier.

We used to patch the verified entry point to make sure it was not_entrant.  The patched entry point then redirected to SharedRuntime::handle_wrong_method(), either directly with a jump to a stub, or indirectly with an illegal instruction and the help of the signal handler.  The not_entrant state is a final state, so once an nmethod becomes not_entrant, it stays not_entrant.  We can do the same thing with a permanently armed nmethod entry barrier.

The solution I went with reserves one bit of the entry barrier guard value.  This bit must remain set, so I call it a "sticky" bit.  Setting the guard value now is effectively like setting a bitfield, so I needed to add a lock around it.  The alternative would be to change the platform-specific code to do compare-and-swap.

For the lock, I introduced a new NMethodEntryBarrier_lock, whose only purpose is to make the update to the guard value atomic.  For ZGC, I decided to use the existing per-nmethod lock ZNMethod::lock_for_nmethod().  I suspect we could do the same for Shenandoah, if needed for performance.

This change also makes it a bit clearer that  the nmethod entry barrier effectively has two levels.  Level 0 is the outer level or layer controlled by BarrierSetNMethod::nmethod_stub_entry_barrier(), and the inner layer controlled by BarrierSetNMethod::nmethod_entry_barrier().  This could be generalized if we decide we need more flavors of entry barriers.  The inner barrier is mostly ignorant of the fact that the outer guard is multiplexing for both levels.

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

Commit messages:
 - cleanup
 - wip

Changes: https://git.openjdk.org/jdk/pull/25764/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25764&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358821
  Stats: 251 lines in 19 files changed: 90 ins; 131 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/25764.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25764/head:pull/25764

PR: https://git.openjdk.org/jdk/pull/25764