Notes on configure

New policies:

• Any 64-bit arch defaults to building whatever the compiler natively does w/o flags unless overridden
• L2SIZE always set to 4MB unless overridden
• Timer defaults to standard wall/cpu unless overridden
  • Exception is solaris, where we default to solaris hr timers
  • If Mhz is passed in, use cycle-accurate wall-timer on x86