+#if defined(darwin_TARGET_OS) && defined(i386_TARGET_ARCH)
+ -- By default, gcc on OS X will generate SSE
+ -- instructions, which need things 16-byte aligned,
+ -- but we don't 16-byte align things. Thus drop
+ -- back to generic i686 compatibility. Trac #2983.
+ ++ ["-march=i686"]
+#endif