extern const char * const
The strsignal() function shall return a pointer to a string describing the signal number sig. The string can only be used until the next call to strsignal().
sys_siglist holds the signal description
strings indexed by signal number. This array should not be accessed
directly by applications.
If sig is a valid signal number, strsignal() shall return a pointer to the appropriate description string. Otherwise, strsignal() shall return either a pointer to the string "unknown signal", or a null pointer.
Although the function is not declared as returning a pointer to a constant character string, applications shall not modify the returned string.