Fold functions for nextafter (#1176)

* Add assertion to prove isNextafter is true iff the builtin is nextafter()

Signed-off-by: Marco Antognini <marco.antognini@arm.com>

* Fold functions for nextafter

There is no need to differentiate nextafter() from other binary builtin
functions when creating the vtbl entries.

Signed-off-by: Marco Antognini <marco.antognini@arm.com>
3 files changed