configure: use correct ASFLAGS for yasm on Solaris
configure: use correct ASFLAGS for yasm on Solaris

stps/libass,Akemi/libass,grigorig/libass,libass/libass,grigorig/libass,mwgoldsmith/libass,astiob/libass,libass/libass,ShiftMediaProject/libass,stps/libass,MrSmile/libass,ShiftMediaProject/libass,Akemi/libass,xbmc/libass,stps/libass,Akemi/libass,xbmc/libass,MrSmile/libass,mwgoldsmith/libass,astiob/libass,mwgoldsmith/libass