[SimplifyCFG] Allow SimplifyCFG hoisting to skip over non-matching instructions

SimplifyCFG does some common code hoisting, which is limited to hoisting a
sequence of identical instruction in identical order and stops at the first
non-identical instruction.

This patch allows hoisting instruction pairs over same-length sequences of
non-matching instructions. The linear asymptotic complexity of the algorithm
stays the same, there's an extra parameter `simplifycfg-hoist-common-skip-limit`
serving to limit compilation time and/or the size of the hoisted live ranges.

The patch improves SPECv6/525.x264_r by about 10%.

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D129370