Reduce warnings by using variables to debug_print(..)

[lifflander]

This is related to #329: enabling all warning by default. The debug_print macro, when disabled, does not "use" the variables passed to it from a static compiler analysis perspective. This causes spurious warnings about unused variables that are used in a debug configuration.

Modify debug_print to always use its arguments, even when its disabled.

There are two possible solutions:

1. Re-write the debug_print macro to recursively use the variables doing something like this. While this approach works (void)(a) recursively accessing each variable in the macro will be expensive from a cpp perspective.

 #define use_it(a) (void)(a);

2. Use a C++ parameter pack to recursively use the args.

    template <typename... Args>
    struct A;
    
    template <typename T, typename... Args>
    struct A<T, Args...> {
      static void forceUseArgs(T&& tp, Args&&... args) {
    	(void)(tp);
    	A::forceUseArgs<Args>(std::forward<Args>(args)...);
      }
    };
    
    template <>
    struct A<> {
      static void forceUseArgs() {  }
    };

@nlslatt @PhilMiller

[lifflander]

I have an implementation now. I have tested (with multiple compilers and versions) that it does not output any code when optimization is turned on. Take a look:

https://godbolt.org/z/ZbGpNL

[lifflander]

Merged, closing