[Bug c/93410] [9 only] can't use _Decimal64 in C99/C11/C17 mode

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93410

--- Comment #3 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to jos...@codesourcery.com from comment #2)
> But that's not the sort of change we make on past release branches.

OK, but note that the GCC manual does not mention any limitation of this kind.
This is rather confusing.