[Bug target/79137] Improve powerpc vector permutes

[wschmidt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79137

--- Comment #1 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
vec_perm_const<n> is one of the standard pattern names, that gets expanded from
a middle-end vector permute.