Trac #15441: Clean up ecl SIGCHLD configuration

Switch from patching ecl to using `ecl_set_option(ECL_OPT_TRAP_SIGCHLD,
0)`.

This ticket was originally a part of #14636.

URL: http://trac.sagemath.org/15441
Reported by: vbraun
Ticket author(s): Volker Braun, Julien Puydt
Reviewer(s): Jean-Pierre Flori