HTT on current

[Yamada Ken Takeshi]

  JYI,
  I tested machdep.hlt_logical_cpus=0/1, buildworld, 
and found no particular reason to disable HTT 
as below with Zeon 2.8Ghz x 2, 1GBmem, Slow IDE HDD.

 It may not be the common case, so just for your info.

# sysctl machdep.hlt_logical_cpus=0
# /usr/bin/time make -j32 buildworld
     1910.29 real      2520.53 user       777.30 sys

# sysctl machdep.hlt_logical_cpus=1
# /usr/bin/time make -j32 buildworld
     2289.33 real      2666.66 user       645.88 sys