Fixes the following build failure:
src/runtime/haskell/Data/Binary/IEEE754.lhs:256:17:
Could not deduce (Num a) arising from a use of `mask'
from the context (Bits a)
bound by the type signature for
clamp :: Bits a => BitCount -> a -> a
The default binary representation in haskell's Data.Binary package is
homemade and quite complicated. Making it compliant with IEEE 754 will
make it easyer for the java runtimes (and probably others) to load the
PGF.