Add a warning to catch a bug recently caught by code review, like this:

Add a warning to catch a bug recently caught by code review, like this:
t2.c:2:12: warning: use of logical && with constant operand; switch to bitwise &
      or remove constant [-Wlogical-bitwise-confusion]
  return x && 4;
           ^  ~

wording improvement suggestions are welcome.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@108260 91177308-0d34-0410-b5e6-96231b3b80d8