MFC r249846:

When rebooting (exiting) from the BTX loader, make sure to restore the
GDT from the correct segment, otherwise a triple fault would be caused.
In some virtual environments (VMware, VirtualBox, etc) this could lead
to a unhandled error or hang in the guest emulation software.

Thanks to avg and jhb for a few hints in the right direction.

Noticed by:	Jeremy Chadwick <jdc@koitsu.org> (and many others)
MFC r249815

Return a lun count of 1 and a lun id of 0 when CAM attempts a REPORT_LUNS
command on a disk device.  This quieseces some noise on the console that
recently appeared.
MFC r250392:

For some reason, the gcc intrinsics header tmmintrin.h was imported with
two copies of itself pasted together.  Remove the extraneous copy.
Tidy up some CVS workarounds.
MFC r250393:

When gcc 4.2.0 was imported, the 3DNow intrinsics header <mm3dnow.h> was
not added to the list of intrinsics headers to install, so belatedly (5
years :) add it.