Add sigemptyset, sigfillset, sigaddset, sigdelset and sigismember with
FreeBSD 11 semantics (lib/libc/gen/sigsetops.c): a 128-bit set of four
32-bit words, signal n at bit n - 1, signals 1 to 128 valid. sigfillset
sets every bit. An invalid signal returns -1 with errno EINVAL and leaves
the set untouched; sigismember returns 1 or 0. A null set throws.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Jan Šlégl