autoconf: lowercase variables
autoconf: lowercase variables

Use lowercase variable names to avoid bogus "possibly undefined macro"
errors.

sanyaade-g2g-repos/libass,sanyaade-g2g-repos/libass,pigoz/libass-ct,blinkseb/libass,pigoz/libass-ct,libass/libass,torque/libass,MrSmile/libass,pigoz/libass-ct,astiob/libass,asimonov-im/libass,libass/libass,rhlee/libass,grigorig/libass,stps/libass,MrSmile/libass,tgoyne/libass,blinkseb/libass,rhlee/libass,stps/libass,richardpl/libass,Distrotech/libass,richardpl/libass,grigorig/libass,sanyaade-g2g-repos/libass,mwgoldsmith/libass,Akemi/libass,asimonov-im/libass,blinkseb/libass,richardpl/libass,Distrotech/libass,xbmc/libass,torque/libass,astiob/libass,Akemi/libass,torque/libass,stps/libass,rhlee/libass,Distrotech/libass,ShiftMediaProject/libass,tgoyne/libass,ShiftMediaProject/libass,mwgoldsmith/libass,tgoyne/libass,mwgoldsmith/libass,xbmc/libass,Akemi/libass