where we had 'noreturn' etc. but no '__noreturn__')
* Scan for __attribute__((bounded)) and __attribute__((used))
if we have __attribute__((noreturn))
* To be able to scan if certain attributes give warnings,
scan for -Werror with a simple programme which hopefully triggers none
* Convert __attribute__((unused)) to __unused, noreturn -> __dead
* Unify other attributes
* Clean up typography a little more
