warnings from backtrace

[Hal Murray]

> As explained in the email: force a seccomp failure, see if the output looks
> better to you.  The output should be improved a bit, if you have seccomp but
> no execinfo.h  Improved with a backtrace if you have execinfo.h. 

I changed the
  #ifdef ENABLE_DNS_LOOKUP
to
  #ifdef xENABLE_DNS_LOOKUP

 1 Jun 21:39:02 ntpd[12595]: sandbox: seccomp enabled.
 1 Jun 21:39:03 ntpd[12595]: dns_probe: trap, cast_flags:8, flags:1
Bad system call

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We should come up with some official way to trigger a backtrace.

Should we add a new command line switch?  Or hack in something like generate 
a backtrace on --version or --help if debug is non-zero.


-- 
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