saving and restoring ia32 specific registers when switching
context and ia32 support has not been compiled-in. The primary
reason for this change is that one of the ia32 registers (ar.fcr)
is wrongly marked as invalid by the simulator. Now that we avoid
using the register when possible, usability is improved. The
secundary reason is that it saves us 7 loads and stores.
Note that the PCB will continue to have room for these registers,
irrespective of the IA32 option. There are no benefits that make
it worthwhile.