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

[joseph at codesourcery dot com]

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

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Fri, 24 Jan 2020, pinskia at gcc dot gnu.org wrote:

> I doubt GCC 9 is going to change.

Indeed.  The old approach was inconsistent with normal practice, as I said 
in commit fe2bc27cdb6d572da0163d77e787ba644b400753 (r276896, "Support 
_Decimal* keywords for C2x."):

    The _Decimal* keywords are marked with D_EXT, meaning they are not
    considered keywords at all in strict conformance modes.  This is
    contrary to the normal practice for most implementation-namespace
    keywords, which are accepted in all standards modes but with
    appropriate pedwarns for older standards.  This patch removes D_EXT
    from those keywords so they are accepted as keywords for all
    standards, consequently removing the gcc.dg/dfp/keywords-ignored-c99.c
    test that is no longer valid.

But that's not the sort of change we make on past release branches.