This part of the tests does pass on glibc on x86_64 and on MSVC,
but fails on macOS (for some functions) and on glibc on aarch64
(for one function).
This is a somewhat overly pedantic test, but is useful for checking
the NAN preservation behaviour when modifying implementations.
Also print the sign bit explicitly - not all printf implementations
distinguish between NAN and -NAN when printed.