waffle: add waffle_get_current_*() functions to waffle.def.in
waffle: add waffle_get_current_*() functions to waffle.def.in

This fixes the MinGW build.

Reviewed-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>

dcbaker/waffle,waffle-gl/waffle,waffle-gl/waffle,dcbaker/waffle,waffle-gl/waffle,dcbaker/waffle,waffle-gl/waffle