[Bug libquadmath/78214] nanq() does not return a quiet NaN

[levim at php dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78214

--- Comment #1 from Levi Morrison <levim at php dot net> ---
Perhaps a less error-prone way to set that same bit is:

    UINT64_C(0x1) << 47

Not sure what would be preferred.