idct_sse2_xvid: only mark xmm>=8 as clobbered on x86_64

Originally committed as revision 25614 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/x86/idct_sse2_xvid.c

@@ -382,9 +382,11 @@ inline void ff_idct_xvid_sse2(short *block)
     :
     : "%eax", "%ecx", "%edx", "%esi", "memory"
       XMM_CLOBBERS(, "%xmm0" , "%xmm1" , "%xmm2" , "%xmm3" ,
-                     "%xmm4" , "%xmm5" , "%xmm6" , "%xmm7" ,
-                     "%xmm8" , "%xmm9" , "%xmm10", "%xmm11",
+                     "%xmm4" , "%xmm5" , "%xmm6" , "%xmm7")
+#if ARCH_X86_64
+      XMM_CLOBBERS(, "%xmm8" , "%xmm9" , "%xmm10", "%xmm11",
                      "%xmm12", "%xmm13", "%xmm14")
+#endif
     );
 }