Extend -Wtautological-constant-out-of-range-compare to handle boolean values

better.  This warning will now trigger on the following conditionals:

bool b;
int i;

if (b > 1) {}  // always false
if (0 <= (i > 5)) {} // always true
if (-1 > b) {} // always false

Patch by Per Viberg.

llvm-svn: 205608