Function sigfillset 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn sigfillset(set: *mut sigset_t) -> c_int

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/sigfillset.html.

Initializes the signal set pointed to by set, such that all signals defined in POSIX.1-2024 are included.

Upon success, returns 0. Upon failure, returns -1 and sets errno to indicate the error.