Add O_EXITKILL to ptrace options.
Add O_EXITKILL to ptrace options.

This prevents a race before PDEATH_SIG can take effect during
a sentry crash.

Discovered and solution by avagin@.

PiperOrigin-RevId: 254871534

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor