built-in functions

[Bruno Schneider]

Hi, I'm trying to compile code with the __builtin_uadd_overflow function. I'm 
using g++ 4.9.2. However, the compiler tells me it is not declared.

Thinking it could be some restriction to g++, I made a tiny C program with the 
function. Then gcc compiled it, but did not link (undefined reference to 
`__builtin_uadd_overflow').

How can I use this function? Can I use it on a C++ program?