Originally I made those as macros. However we have many
other small functions like mp_clamp, mp_exch which are also not implemented
as macros right now.
If we would use c99, I would implement them as private static inline
functions. And mp_exch would be a public static inline function.
But since we are bound to c89, we simply use normal functions.
To achieve optimal performance one should either use link time
optimization or amalgamation.
* This gives the advantage that static analysis **understands** bool,
but complains about using an enum type instead of bool.
* If stdbool.h is not desired, true/false/bool can be replaced using sed
as in the no-stdint-h branch.
* We already include stdint.h and stdbool.h is not more harmful than
this header
