Optimize for Intel Pentium 4, Pentium D and older Nocona/Dempsey
Xeon CPUs with Intel 64bit which is compatible with x86-64.
Note that the latest Xeons (Xeon 51xx and 53xx) are not based on the
Netburst core and shouldn't use this option. You can distinguish them
using the cpu family field
in /proc/cpuinfo. Family 15 is an older Xeon, Family 6 a newer one.