https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65757
--- Comment #9 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- Fixed in glibc (commit 7d0b2575416aec2717e8665287d0ab77826a0ade). I'd advise merging to trunk GCC libquadmath all relevant glibc changes since the last merges in 2012, rather than cherry-picking just this fix (although if you wish to fix things on release branches, cherry-picking just the critical fixes would be appropriate there).
