fatal-signal: Remove dependency upon xalloc. * lib/fatal-signal.h (at_fatal_signal): Change return type to 'int'. * lib/fatal-signal.c: Don't include xalloc.h. (at_fatal_signal): Return an error indicator. * modules/fatal-signal (Depends-on): Remove xalloc. * NEWS: Mention the change. * lib/term-style-control.c: Include xalloc.h. (ensure_other_signal_handlers): Test return value of at_fatal_signal. * lib/clean-temp.c (do_init_clean_temp): Likewise. * lib/wait-process.c (register_slave_subprocess): Likewise. * modules/term-style-control (Depends-on): Add xalloc-die. * modules/clean-temp (Depends-on): Likewise. * modules/wait-process (Depends-on): Likewise.