Set mm_flags in dct-test to fix floating math.

Patch by Alexander Strange \astrange ithinksw com/

Originally committed as revision 12580 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dct-test.c

@@ -531,6 +531,7 @@ int main(int argc, char **argv)
 
     init_fdct();
     idct_mmx_init();
+    mm_flags = mm_support();
 
     for(i=0;i<256;i++) cropTbl[i + MAX_NEG_CROP] = i;
     for(i=0;i<MAX_NEG_CROP;i++) {