Add Zero Heurestics to BranchProbabilityInfo. If we compare value to zero we

decide whether condition is likely to be true this way:

x == 0  ->  false
x <  0  ->  false
x <= 0  ->  false
x != 0  ->  true
x >  0  ->  true
x >= 0  ->  true

llvm-svn: 136583