It matters less than you think. The entire point of e.g. DO-178C is to achieve high assurance that the code performs it's intended function. Basically, you need to be able to trace your object code to system level requirements. You need to achieve 100% MC/DC coverage from requirements based testing. If there's something you don't cover you either remove the code, or add derived requirements (which need to be assessed by the systems safety process). Language choice doesn't remove any of the objectives you need to achieve.

Also, keep in mind that the desire to have a deterministic system puts a lot of constraint on what kind of behavior you can program anyway.