Currently, all inputs are generated and then cached. This works
reasonably well but it isn't very configurable or extensible (adding
`f16` and `f128` is awkward).
Replace this with a trait for generating random sequences of tuples.
This also removes possible storage limitations of caching all inputs.
Once we start addinf `f16` and `f128` routines, we will need to have
this cfg for almost all uses of `for_each_function`. Rather than needing
to specify this each time, always emit `#[cfg(f16_enabled)]` or
`#[cfg(f128_enabled)]` for each function that uses `f16` or `f128`,
respectively.
Check our functions against `musl-math-sys`. This is similar to the
existing musl tests that go through binary serialization, but works on
more platforms.
