Define mm_flags/support to be 0 on architectures where they don't exist.

Make sure we don't try to set them if that's the case.
This lets dct-test and fft-test build with --disable-mmx on x86, but not yet on ARM.

Originally committed as revision 13957 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/fft-test.c

@@ -186,7 +186,10 @@ int main(int argc, char **argv)
     MDCTContext m1, *m = &m1;
     int fft_nbits, fft_size;
 
+#ifndef mm_flags
     mm_flags = 0;
+#endif
+
     fft_nbits = 9;
     for(;;) {
         c = getopt(argc, argv, "hsimn:");