The point really was that the unused method parameter should in almost all cases be removed, not that some trick should be used to make it seem used, and this is the wrong trick!

Sometimes. But sometimes you have a set of functions that are called through function pointers that need the same signature, and one or more of them ignore some of the arguments. These days I’d spell that __attribute__((unused)); but it’s a perfectly reasonable case.

    #if otherbuild
        dosomething(param);
     #endif

the above type of thing happens once in a while. nos the paramater is needed but the normal build doesn't use it

I'm sure thats disallowed for the C-style cast.

Fwiw, unused-cast-to-void is a case that GCC and Clang ignore when using -Wno-old-style-cast, which is what most projects prohibiting C-style casts are going to be using (or whatever the equivalent their compiler provides).

C++17 has the [[maybe_unused]] attribute.