Select a strategy to mitigate speculative bounds check bypass (aka Spectre-PHT or Spectre V1).
This is an experimental option - execution of untrusted code is not supported by GraalVM CE.
The accepted values are:
                  None - No mitigations are used in JIT compiled code.
            AllTargets - Speculative execution on all conditional branch targets is
                         stopped using speculative execution barrier instructions.
          GuardTargets - Branch targets relevant to Java memory safety are instrumented
                         with barrier instructions. This option has less performance impact
                         than AllTargets. Note that memory accesses through UNSAFE are not
                         covered by this mitigation. This includes libraries built upon UNSAFE,
                         such as java.nio.ByteBuffer.
  NonDeoptGuardTargets - Same as GuardTargets, except that branches which deoptimize are not
                         protected since they can not be executed repeatedly and are thus less
                         likely to be successfully exploited in an attack.
