Add missing load/store flags to thumb2 instructions.

These were the cause of a verifier error when building 7zip with
-verify-machineinstrs.  Running 'make check' with the verifier
triggered the same error on the test here so i've updated the test
to run the verifier on one of its runs instead of adding a new one.

While looking at this code, there was a stale comment that these
instructions were only used for disassembly.  This probably used to
be the case, but they are now used in the 'ARM load / store optimization pass' too.

This reapplies r242300 which was reverted in r242428 due to bot failures.

Ultimately those failures were spurious and completely unrelated to this commit.  I reverted this
at the time because it was thought to be at fault.

llvm-svn: 250969