[Bug tree-optimization/91151] new test case gcc.dg/tree-ssa/vector-7.c fails with its introduction in r273435

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91151

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Bah, I didn't actually test the BIG_ENDIAN case ... can you maybe check it and
fix it up or report whether it actually miscompiles?