Under MVE, we do not have any lowering for fminimum, which a vector_reduce_fmin without NoNan will be expanded into. As with the other recent patches, force this to expand in the pre-isel pass. Note that Neon lowering would be OK because the scalar fminimum uses the vector VMIN instruction, but is probably better to just rely on the scalar operations, which is what is done here.
Also fixes what appears to be the reversal of INF vs -INF in the vector_reduce_fmin widening code.