This commit addresses a seemingly unintentional return type of the ilogb
overload taking a double. Currently it returns double, while it is
supposed to return int.
The return types seems to be covered by libcxx/test/std/numerics/c.math/cmath.pass.cpp,
but the issue would only show up if we tested with a libc that doesn't
provide the ilogb(double) overload, which we don't.
09cc8eaf1b