[Bug target/70734] __builtin_add_overflow emits poor code on x86-64

[arigo at tunes dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70734

--- Comment #4 from Armin Rigo <arigo at tunes dot org> ---
Ah, sorry about that; I only checked the 5.x branch.  My mistake.