[Bug middle-end/124491] [14/15 Regression] ICE in fold_vec_perm during ccp with -msve-vector-bits=256

[acoplan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124491

--- Comment #4 from Alex Coplan <acoplan at gcc dot gnu.org> ---
So the cherry-picks of:

847155f2ca2 middle-end/123573 - fix VEC_PERM folding more
62149da4a20 middle-end/123175 - fix parts of const VEC_PERM with relaxed input
sizes

to the 15 branch also survived bootstrap & regtest on aarch64.  OK to push
those to GCC 15?  I suppose we should add an aarch64 test with the testcase
from #c0 too, I can prepare a patch to do that.