Select a strategy to mitigate speculative execution attacks (e.g., SPECTRE).
The accepted values are:
                  None - No mitigations are used in JIT compiled code.
            AllTargets - All branches are protected against speculative attacks.
                         This has a significant performance impact.
          GuardTargets - Only branches that preserve Java memory safety are protected.
                         This has less performance impact than AllTargets.
  NonDeoptGuardTargets - GuardTargets except that branches which deoptimize are not
                         protected since they can not be executed repeatedly.
