less /usr/share/examples/etc/make.conf
...
# The CPUTYPE variable controls which processor should be targeted for
# generated code. This controls processor-specific optimizations in
# certain code (currently only OpenSSL) as well as modifying the value
# of CFLAGS to contain the appropriate optimization directive to gcc.
# The automatic setting of CFLAGS may be overridden using the
# NO_CPU_CFLAGS variable below.
# Currently the following CPU types are recognized:
# Intel x86 architecture:
# (AMD CPUs) opteron-sse3 opteron athlon64-sse3 athlon64 athlon-mp
# athlon-xp athlon-4 athlon-tbird athlon k8-sse3 k8
# geode k6-3 k6-2 k6 k5
CPUTYPE?=k6-2