[Bug c++/91304] maybe_unused attribute ignored on variable declared in if declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91304

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to fsmoke from comment #6)
> I am sorry..I am new in gcc bugzilla. But.. i have gcc 9.3 and this issue
> still takes a place.

Because it's fixed in GCC 10.1