[Bug target/88234] UBsan and runtime error: signed integer overflow using unsigned vector

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88234

--- Comment #6 from Marc Glisse <glisse at gcc dot gnu.org> ---
#define vec_add(a,b) ((a)+(b))

IIRC that only fails for __vector bool, but I think the ppc people didn't like
this approach.