expr: Limit the store flag optimization for single bit to non-vectors [PR113322]
The problem here is after the recent vectorizer improvements, we end up
with a comparison against a vector bool 0 which then tries expand_single_bit_test
which is not expecting vector comparisons at all.
The IR was:
vector(4) <signed-boolean:1> mask_patt_5.13;
_Bool _12;