[LICM] Simplify (X < A && X < B) into (X < MIN(A, B)) if MIN(A, B) is loop-invariant

[LICM] Simplify (X < A && X < B) into (X < MIN(A, B)) if MIN(A, B) is loop-invariant

We don't do this transform in InstCombine in general case for arbitrary values, because cost of
AND and 2 ICMP's isn't higher than of MIN and ICMP. However, LICM also has a notion
about the loop structure. This transform becomes profitable if `A` and `B` are loop-invariant and
`X` is not: by doing this, we can compute min outside the loop.

Differential Revision: https://reviews.llvm.org/D143726
Reviewed By: nikic