Multiply-add with minus signs doesn't get converted to muladd

[ikirill]

I expected this to work, but it didn't. There is generally no problem with having minus signs inside muladd, because FMA instructions allow for that, so expressions like b-a*x should be converted to muladd(-a, x, b).

julia> macroexpand(:(MuladdMacro.@muladd b - a * x))
:(b - a * x)

julia> macroexpand(:(MuladdMacro.@muladd b + a * x))
:((muladd)(a, x, b))

[ChrisRackauckas]

Yeah, it looks like we're missing this. We're looking directly for +s and handling that. I'm not sure the easiest way to implement this.