Stop using SIG_0

Stop using SIG_0

Number 0 is not a valid signal number, and SIG_0 is not a valid
description for a signal.

* linux/signalent.h: Replace SIG_0 with 0.
* linux/alpha/signalent.h: Likewise.
* linux/hppa/signalent.h: Likewise.
* linux/mips/signalent.h: Likewise.
* linux/sparc/signalent.h: Likewise.
* filter_qualify.c (sigstr_to_uint): Start iterations with number 1.
* tests/fcntl-common.c (test_fcntl_others): Update expected output.
* tests/kill.c (main): Likewise.
* tests/ptrace.c (test_peeksiginfo): Likewise.
* tests/s390_runtime_instr.c (main): Likewise.