Linux sandbox: restrict *kill to the current process.

sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h

Index: sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
diff --git a/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h b/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
index b8f626aec613c496564fb8a20ac54ab3ca52fe55..fdfbb66c5b83038b4e1dd819a7367a43d6e7f79b 100644
--- a/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
+++ b/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
@@ -38,6 +38,9 @@ SANDBOX_EXPORT intptr_t
 // argument.
 SANDBOX_EXPORT intptr_t
     SIGSYSIoctlFailure(const struct arch_seccomp_data& args, void* aux);
+// The crashing address will be (pid & 0xFFF), where pid is the first
+// argument (and can be a tid).
+intptr_t SIGSYSKillFailure(const struct arch_seccomp_data& args, void* aux);
 
 // Following four functions return substrings of error messages used
 // in the above four functions. They are useful in death tests.