Paul Eggert wrote:

> I have thought of a solution that fixes the problem by dropping use of GCALIGNED 
> and instead using classic C unions along with 'char alignas (8)'.

Patches attached. They work for me on various platforms including gcc -m32 on 
Fedora 26 x86-64 (which is close to the platform Glenn mentioned). The 2nd patch 
does the real work: most of it consists of changing private accessors to account 
for the newly-introduced unions. It shrinks the source code a bit, which is a 
good sign. I plan to test a bit more before installing; comments welcome.