8361376: Regressions 1-6% in several Renaissance in 26-b4 only MacOSX aarch64

[dean-long]

This PR removes the recently added lock around set_guard_value, using instead Atomic::cmpxchg to atomically update bit-fields of the guard value. Further, it takes a fast-path that uses the previous direct store when at a safepoint. Combined, these changes should get us back to almost where we were before in terms of overhead. If necessary, we could go even further and allow make_not_entrant() to perform a direct byte store, leaving 24 bits for the guard value.

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Issue

• JDK-8361376: Regressions 1-6% in several Renaissance in 26-b4 only MacOSX aarch64 (Bug - P4)

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• 00: Full (ecc6e68e)