[Bug c++/108052] forward-declared constexpr variable template unusable in constexpr context

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108052

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note clang also rejects the double case just as GCC does and accepts the int
case too.

MSVC accepts both the int and double case.