init: use a no-op signal handler instead of SIG_IGN for SIGPIPE

We want to ignore SIGPIPE within init, but if we use SIG_IGN, that
would be inherited by child processes through exec(), which we do not
want to have happen.  We instead set up a real signal handler with a
no-op handler function, that will ignore SIGPIPE within init, but will
not be inherited across exec().

This fixes c29c2baa ("init: Add support for native service
registration with lmkd"), when SIG_IGN was introduced.
Note that we caught this issue before shipping a release with that
change, so the major motivation here is to not cause a behavior change
in init.

Bug: 151581751
Test: children of init that don't explicitly block SIGPIPE exit when
      sent SIGPIPE
Test: children of init that do explicitly block SIGPIPE do not exit
      when sent SIGPIPE
Test: init does not exit when sent SIGPIPE
Test: init exits when sent SIGABRT
Change-Id: Ieda8555fd03836bcd672a422fe673a8369ad9beb