Significant changes to correctly spill CC registers and to correctly

Significant changes to correctly spill CC registers and to correctly
handle conditional move instructions:
-- cpMem<->Reg functions now support CC registers (int and FP) correctly.
-- Scratch registers must be explicitly provided to cpMem<->Reg when
   needed, since CC regs need one to be copied to/from memory.
-- CC regs are saved to a scratch register instead of stack.
-- All regs used by a instruction are now recorded in MachineInstr::regsUsed,
   since regs used to save values *across* an instruction are not obvious
   either from the operands or from the LiveVar sets.
-- An (explicit or implicit) operand may now be both a def and a use.
   This is needed for conditional move operations.
   So an operand may need spill code both before and after the instruction.
-- class MachineCodeForBasicBlock is now an annotation on BasicBlock.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2833 91177308-0d34-0410-b5e6-96231b3b80d8