ppc64le: gcc 12 vs -mabi=ibmlongdouble

[Florian Weimer]

* Paul E. Murphy:

> On 1/24/22 9:38 AM, Florian Weimer wrote:
>> * DJ Delorie via Libc-alpha:
>> 
>>> I've been working on updating glibc for Fedora Rawhide, and have
>>> stumbled upon this issue (after working around the -Wuse-after-free
>>> issues with a cflags hack)...  A few of the math tests explicitly add
>>> -mlong-double-64 but configure adds -mabi=ibmlongdouble
>>>
>>> I would guess that we need a "CFLAGS -= -mabi=ibmlongdouble" in all
>>> the places we add -mlong-double-64 but I don't see an easy way of
>>> doing that, nor am I sure that's a valid solution.  Alternately, gcc
>>> could be changed to accept the conflicting flags in a meaningful way,
>>> if there is one.  Is there an -mabi= that undoes the
>>> -mabi=ibmlongdouble that we can just add to the -mlong-double-64 flag
>>> lines?
>
> For the sake of my clarification, does this affect more than the 6
> test cases/files in ldbl-opt Makefile? If not, could the removal be
> handled case-by-case in sysdeps/powerpc/powerpc64/le/Makefile?

That's what I tried in my patch, but it seems to interact negatively
with other make constructs, so any CFLAGS-*.c settings stop working for
these targets.

Thanks,
Florian