add_of - add two integers, check for arithmetic overflow

#include <rangecheck.h>

int add_of(dest,a,b);

If calculating a+b is possible without causing undefined behavior or an arithmetic overflow in C, and the sum fits into the destination integer type, do dest=a+b and return 0.

Otherwise, return 1.

Note: This is a macro, so dest does not have to be a pointer.

In the multiplication functions, a return value of 1 signals success and 0 failure. In add_of, sub_of and assign it's the other way around.

sub_of(3), assign(3), imult16(3), umult16(3), imult32(3), umult32(3), imult64(3), umult64(3),