unix: posix: avoid use of variadic macro `p_snprintf` The macro `p_snprintf` is implemented as a variadic macro that calls `snprintf` directly with `__VA_ARGS__`. In C89, variadic macros are not allowed, but as the arguments of `p_snprintf` and `snprintf` are matching 1:1, we can fix this by simply removing the parameter list from `p_snprintf`.