Convert typeof keyword into __typeof__; this is a gcc extension and the former is not accepted in C99 without GNU extensions enabled (e.g. via -fasm).  This fixes compilation on PPC.

git-svn-id: file:///var/local/repositories/mplayer/trunk/libswscale@27805 b3059339-0415-0410-9bf9-f77b7e298cf2