Disallow side effects in assert

[bearophile]

Marco Leise:

> Damn those gotchas. Basically lock.try_acquire is pure when it
> returns false, and if not, the program is terminated anyways so
> it doesn't make a difference.

So an annotation like the proposed @noreturn (similar to GCC 
function annotation, and useful for functions that do not return, 
so they can be used where you use assert(0) and the like) is not 
enough to solve this problem.

Bye,
bearophile