[Bug c++/107111] GCC accepts invalid program involving function declaration with pack expansion

[jlame646 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107111

--- Comment #5 from Jason Liam <jlame646 at gmail dot com> ---
Note also that gcc accepts `T v(V...b())` but rejects `T v(V...())`. Note the
use of parameter name in the former. Demo: https://godbolt.org/z/hMevdc8TE