Recommit r317510 "[InstCombine] Pull shifts through a select plus binop with constant"

The hexagon test should be fixed now.

Original commit message:

This pulls shifts through a select+binop with a constant where the select conditionally executes the binop. We already do this for just the binop, but not with the select.

This can allow us to get the select closer to other selects to enable removing one.

Differential Revision: https://reviews.llvm.org/D39222

llvm-svn: 317600