[APInt] Keep the original bit width in quotient and remainder

[APInt] Keep the original bit width in quotient and remainder

Some trivial cases in udivrem were handled by directly assigning 0 or 1
to APInt objects. This would set the bit width to 1, instead of the bit
width of the inputs. A potentially undesirable side effect of that is
that with the bit width of 1, 1 equals -1.

Differential Revision: https://reviews.llvm.org/D49554

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337478 91177308-0d34-0410-b5e6-96231b3b80d8