1. Make internal functions take const arguments where they should, just

   to be safe.
2. Make internal functions that return a carry/borrow return bool instead
   of uint64_t because the carry/borrow can only be in range [0,1].
3. Assert that the pointers to KnuthDiv are all different so that the
   result and operands can't overlap.
4. Add debug output to KnuthDiv function.
5. Fix a problem with KnuthDiv by separating the b's complement operation
   from the subtraction borrow operation. This fixes a wide range of
   division problems, but alas, not all of them.

llvm-svn: 34554