[ARM] Transfer the internal flag in thumb2 size reduction.

Converting from t2LDRs to tLDRr caused the shift argument to drop the internal flag.  This would then throw machine verifier errors.

Unfortunately i'm having trouble reducing a test case.  I'm going to keep trying, but so far its a scary combination of machine sinking, an 'and i1', loads feeding loads, and a bunch of code which shouldn't change IT block formation, but does.  Its not useful to commit a test in that state as we have no way of knowing if it even hits this code reliably in future.

rdar://problem/20752113

llvm-svn: 236333