[Bug c++/71753] Clamp function does not work with O3 optimization

[lukasz.spintzyk at displaylink dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71753

--- Comment #4 from Łukasz Spintzyk <lukasz.spintzyk at displaylink dot com> ---
Yes, this code is utilizing overflow, but it is there for a reason to optimize
the code and get rid of branches as they can slow down program execution.

You can refer to http://locklessinc.com/articles/sat_arithmetic/

Looking from this point of view is this really invalid?