[Bug target/88529] G++ clears the return register on x86_64 when returning an empty class

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88529

--- Comment #5 from Antony Polukhin <antoshkka at gmail dot com> ---
(In reply to Jason Merrill from comment #1)
> Created attachment 45899 [details]
> Fix

Is it enough to test only for `scan-assembler-not mov`? Probably a
`scan-assembler-not xor` should be also added?