[Bug c++/109367] bogus -Wunused-function warning with decltype of a lambda as an argument

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109367

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually I think the bug is:
using T = decltype ([]{});

is broken with GCC. There are multiple testcases dealing with that even.