In binary_float.cpp, copysign is special cased. All the reference
functions there take double arguments, except for reference_copysign
which takes float. This commit copies that approach to special case
copysign in binary_double.cpp as well: all the reference functions there
take long double arguments, but this commit changes reference_copysignl
to take double. The rationale for this in binary_float applies equally
to binary_double: conversions of NAN are not required to preserve its
sign bit. On architectures where conversion of NAN resets the sign bit,
copysign fp64 would return incorrect reference results.
80a02cbd48