Isn't it always true on x86_64 that you have sse?
+#ifdef ARCH_X86_64
+ if (gCpuCaps.hasSSE)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ {
+ dct64_MMX_func = dct64_sse;
+ mp_msg(MSGT_DECAUDIO,MSGL_V,"mp3lib: using SSE optimized decore!\n");
+ }
+ else
+#endif