[X86] Making X86OptimizeLEAs pass public. NFC

Reviewers: wxiao3, LuoYuanke, andrew.w.kaylor, craig.topper, annita.zhang, liutianle, pengfei, xiangzhangllvm, RKSimon, spatel, andreadb

Reviewed By: RKSimon

Subscribers: andreadb, hiraditya, llvm-commits

Tags: #llvm

Patch by Gen Pei (gpei)

Differential Revision: https://reviews.llvm.org/D65933

llvm-svn: 369612