Extern data

# extern.C 'x': T — a C global (decided 2026-09-21). Reading or writing it is a no_check site.
extern.C 'lib_version': int32;              # C: extern int lib_version;
extern.C mut 'lib_verbose': int32;          # C: extern int lib_verbose;  (we may write it)

MAIN {
    no_check let 'v' := 'lib_version';
    std::print.useful["version ", 'v', newln];
    no_check change 'lib_verbose' = 1;
    no_check let 'on' := 'lib_verbose';
    std::print.useful["verbose ", 'on', newln];
}