Review D88220 turns out to have some pretty severe bugs, but I *think* this patch fixes them.
Paper P1825 is supposed to enable implicit move from "non-volatile objects
and rvalue references to non-volatile object types." Instead, what was committed
seems to have enabled implicit move from "non-volatile things of all kinds,
except that if they're rvalue references then they must also refer to non-volatile
things." In other words, D88220 accidentally enabled implicit move from
lvalue object references (super yikes!) and also from non-object references
(such as references to functions).
These two cases are now fixed and regression-tested.
(For better and worse, D88220 was present in trunk for more than a month before anyone noticed the (very major!) bug — my thanks to @sberg for reporting it! — so we may be able to take our time fixing it, but also it may be another month before someone spots the next bug. I have no strong opinion on the process here.)