test: Correctly check for branch statements

In r250408 'CHECK-NEXT: br' lines were removed as they also matched a
'%polly.subregion.iv.inc' instruction and did consequently not check what they
were supposed to check. However, without these lines we can not test that the
.s2a instructions that are not any more generated since r250411 really are not
emitted. Hence, we add back the CHECK-NEXT lines to ensure there are really no
instructions generated between the store that we check for and the branch at the
end of the basic block. To ensure we do not match too early, we now check for
'br i1' or 'br label'.

llvm-svn: 250435