claim that "st" is from the 80-bit register file. This causes x87-using inline

asm to die with:

ScheduleDAG.cpp:269: failed assertion `false && "Couldn't find the register class"'

instead of:
failed assertion `RegMap->getRegClass(VReg) == RC && "Register class of operand and regclass of use don't agree!"'

yay.

llvm-svn: 42259