25% faster floating point AAN IDCT.

Other float code likely benefits as well ...

Originally committed as revision 12245 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1808,6 +1808,7 @@ elif enabled optimizations; then
         add_cflags "-O3"
     fi
 fi
+check_cflags -fno-math-errno
 
 # PIC flags for shared library objects where they are needed
 if enabled shared; then