[Bug target/71731] incorrect result for vectorized char rotate with -mcpu=power9

[acsawdey at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71731

--- Comment #2 from acsawdey at gcc dot gnu.org ---
This fails with trunk 237811 or later, but that is because power9-dform-vector
was turned on by default there. For instance 237715 also fails this if you add
-mpower9-dform-vector to the flags.