Define HAVE_BIGENDIAN as 0 or 1 according to CPU type

This should replace the inconsistently named and defined
WORDS_BIGENDIAN.

Originally committed as revision 18873 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -866,6 +866,7 @@ HAVE_LIST="
     alsa_asoundlib_h
     altivec_h
     arpa_inet_h
+    bigendian
     bswap
     closesocket
     cmov