dirac: Only use MMX if MMX is available.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/x86/diracdsp_mmx.c

@@ -60,6 +60,9 @@ void ff_diracdsp_init_mmx(DiracDSPContext* c)
 {
     int mm_flags = av_get_cpu_flags();
 
+    if (!(mm_flags & AV_CPU_FLAG_MMX))
+        return;
+
 #if HAVE_YASM
     c->add_dirac_obmc[0] = ff_add_dirac_obmc8_mmx;
 #if !ARCH_X86_64