Implemented a warning when an input several bitwise operations are
likely be implicitly truncated:

  * All forms of Bitwise-and, bitwise-or, and integer multiplication.
  * The assignment form of integer addition, subtraction, and exclusive-or
  * The RHS of the comma operator
  * The LHS of left shifts.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178273 91177308-0d34-0410-b5e6-96231b3b80d8