resampler: Work at double precision on x86-64 machines. We get audio artifacts if we don't work at the higher precision, but this is painful on CPUs that have to use a software fallback for this, so for now (that is, until we have a better solution), get better output on amd64 chips, where the cost is less painful. (cherry picked from commit 1e5e8e2fda3796e76e6f7b1c39683925a3e9fed9)