sig.c: Skip unknown signals, e.g. musl libc does not define SIGCLD
sig.c: Skip unknown signals, e.g. musl libc does not define SIGCLD

Signed-off-by: Joachim Nilsson <583c295fd7602c168ad814279bbc3894ba65f5d6@gmail.com>

troglobit/finit,troglobit/finit