We currently do not have any floating point operators where operand 1 is 
a different type than the LHS. When we eventually do there is a bug in 
fold_range. If either operand is a known NAN, it returns a NAN of the 
type of operand 1 instead of the result type.

This patch sets it to the correct type.

Bootstraps on build-x86_64-pc-linux-gnu with no regressions. Pushed.

Andrew