kernel - Misc fixes and debugging

kernel - Misc fixes and debugging

* Add required CLDs in the exception paths.  The interrupt paths already
  CLD in PUSH_FRAME.

* Note that the fast_syscall (SYSENTER) path has an implied CLD due to the
  hardware mask applied to rflags.

* Add the IOPL bits to the set of bits set to 0 during a fast_syscall.

* When creating a dummy interrupt frame we don't have to push the
  actual %cs.  Just push $0 so the frame isn't misinterpreted as coming
  from userland.

* Additional debug verbosity for freeze_on_seg_fault.

* Reserve two void * fields for LWP debugging (for a later commit)