Fix compilation when MMX is disabled.

inspired by a patch by Ronald S. Bultje, rbultje ronald.bitfreak net

Originally committed as revision 9243 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dct-test.c

@@ -91,7 +91,7 @@ struct algo algos[] = {
   DCT_ERROR("INT",             1, j_rev_dct,          idct, MMX_PERM),
   DCT_ERROR("SIMPLE-C",        1, simple_idct,        idct, NO_PERM),
 
-#ifdef ARCH_X86
+#ifdef HAVE_MMX
   DCT_ERROR("MMX",             0, ff_fdct_mmx,        fdct, NO_PERM),
   DCT_ERROR("MMX2",            0, ff_fdct_mmx2,       fdct, NO_PERM),