The compiler instrinsics are exposed via fully specialized template functions
which must not be defined twice (which they accidentally were). Declaring them
as inline fixes this issue.
- templated structs were not required, SFINAE works for functions too
=> use instead, removes some unneeded code
- fix non-usage of builtins with clang
- adjust unit tests
The fallback signed integer overflow check is quite expensive, but the addition
can be safely performed when saved in an int due to integer promotion
rules. This makes the check a little less expensive.
Rosen Penev
Robin Mills
Luis Díaz Más
Dan Čermák