linux-user: Only register handlers for core_dump_signal by default

linux-user: Only register handlers for core_dump_signal by default

The set of fatal signals is really immaterial.  If one arrives,
and is unhandled, then the qemu process dies and the parent gets
the correct signal.

It is only for those signals which we would like to perform a
guest core dump instead of a host core dump that we need to catch.

Acked-by: Helge Deller <deller@gmx.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>