[Bug tree-optimization/15826] don't use "if" to extract a single bit bit-field.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=15826

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Which boils down to the premature fold-const.c:optimize_bit_field_compare
which creates this BIT_FIELD_REF (fold_truth_andor_1 does similar stupid
stuff).