Fixes make checkheaders

Signed-off-by: James Almer <jamrial@gmail.com>

Functions av_gt_sf, av_sqrt_sf and av_sincos_sf added to softfloat

Signed-off-by: Nedeljko Babic <nedeljko.babic@imgtec.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>