[RFC] Use simpler math functions when user selects -ffast-math

[Ondřej Bílka]

Hi Andrew,

When I checked isfinite performance I noticed that for most math
functions wrapper is unnecessary when -ffinite-math-only is set from
-ffast-math as they evaluate to constant.

So if you are still interested at improving math library you could in
similar way as vector math add calls to say fast_sin, fast_cos... I don't
know how to make vectorizer also recognize these so I ask you.

Adding new symbols would allow to fix bug that due accuracy math
functions need to be very slow on some inputs. As with -ffast-math you
don't have to worry much about accuracy we could finally fix these bugs.

So what do you say?