Non-fast-isel followup to 129634; correctly handle branches controlled

Non-fast-isel followup to 129634; correctly handle branches controlled
by non-CMP expressions.  The executable test case (129821) would test
this as well, if we had an "-O0 -disable-arm-fast-isel" LLVM-GCC
tester.  Alas, the ARM assembly would be very difficult to check with
FileCheck.

The thumb2-cbnz.ll test is affected; it generates larger code (tst.w
vs. cmp #0), but I believe the new version is correct.
rdar://problem/9298790

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131261 91177308-0d34-0410-b5e6-96231b3b80d8