Disable the load/store optimization pass for Thumb-1.

Moritz's changes have improved codegen a lot, but further testing showed significant correctness problems. Disable by default until these have been worked out.

Patch by Moritz Roth!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210789 91177308-0d34-0410-b5e6-96231b3b80d8