[Bug rtl-optimization/85925] [7/8/9 regression] compilation of masking with 257 goes wrong in combine at -02

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85925

--- Comment #31 from Segher Boessenkool <segher at gcc dot gnu.org> ---
It needs some certain bitfield layout, so this is not portable and should
only be run for those targets it is meant for (x86?)