Add a flag to disallow floating point reordering

[inducer]

Context: https://github.com/inducer/loopy/pull/698#issuecomment-1306451565

IMO, this should only apply to code generation, not transforms. Transforms can receive permission to ignore FP reordering individually.

Another aspect is that reductions do not even have a defined FP evaluation order (but we could conceivably force one).