[X86] Enable RRL part of the LEA optimization pass for -O2.

Enable "Remove Redundant LEAs" part of the LEA optimization pass for -O2.
This gives 6.4% performance improve on Broadwell on nnet benchmark from Coremark-pro.
There is no significant effect on other benchmarks (Geekbench, Spec2000, Spec2006).

Differential Revision: http://reviews.llvm.org/D19659

llvm-svn: 270036