[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: nikic, dmgreen

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