Add some things needed by the llvm-gcc version supporting bit accurate integer

Add some things needed by the llvm-gcc version supporting bit accurate integer
types:
1. Functions to compute div/rem at the same time.
2. Further assurance that an APInt with 0 bitwidth cannot be constructed.
3. Left and right rotate operations.
4. An exactLogBase2 function which requires an exact power of two or it
   returns -1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37025 91177308-0d34-0410-b5e6-96231b3b80d8