[PATCH v2] sysdeps/ieee754: Fix remainder sign of zero for FE_DOWNWARD (BZ #32711)

[Sergei Zimmerman]

> We have a macro for this, XFAIL_ROUNDING_IBM128_LIBGCC.  So I think it just
> a matter to remove the conditional and use the flag instead.

Thanks for the the guidance and feedback. I've applied your suggestion to v3.