std::pow implementation

[Robert Dewar]

> Gaby, the scenario Alex describes is COMMON.  Constant propagation
> frequently causes lots of code to be thrown away, and any automatic
> inlining decision that doesn't take this effect into account is broken.


Note thjat this is even more the case in Ada, where the normal way of doing
conditional compilation is by the use of constant booleans (there is no
macro preprocessing defined in Ada).