[patch c++]: PR c++/44294 abi/bitfield12.C regression

[Eric Botcazou]

> Are you sure this is safe?  There have often been problems in the past
> with targets using machine modes to determine the function-calling ABI,
> which means that anything that could change the mode assigned to a
> structure or union type is dangerous unless you can show it won't affect
> any targets using modes to determine ABIs.

And the patch is backwards, MAX_FIXED_MODE_SIZE should be used to determine 
whether __int128 is supported for the target, not the other way around.

-- 
Eric Botcazou