[llvm-exegesis] Explore LEA addressing modes.

Summary:
This will help for PR32326.

This shows the well-known issue with `RBP` and `R13` as base registers.

Reviewers: gchatelet

Subscribers: tschuett, llvm-commits, RKSimon, andreadb

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68646

llvm-svn: 374146