[Bug c/64639] false negative of -Wunused-value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
"(a = 0) != 0" has a side effect of setting a to 0.

I think in this case, clang is incorrectly warning about it.