xz: list: suppress -Wformat-nonliteral for Solaris

xz: list: suppress -Wformat-nonliteral for Solaris

Solaris' GCC can't understand that our use is fine, unlike modern compilers:
```
list.c: In function 'print_totals_basic':
list.c:1191:4: error: format not a string literal, argument types not checked [-Werror=format-nonliteral]
  uint64_to_str(totals.files, 0));
  ^~~~~~~~~~~~~
cc1: all warnings being treated as errors
```

It's presumably because of older gettext missing format attributes.

This is with `gcc (GCC) 7.3.0`.