[ARM][LowOverheadLoops] Correct offset checking

[ARM][LowOverheadLoops] Correct offset checking

This patch addresses a couple of problems:
1) The maximum supported offset of LE is -4094.
2) The offset of WLS also needs to be checked, this uses a
   maximum positive offset of 4094.

The use of BasicBlockUtils has been changed because the block offsets
weren't being initialised, but the isBBInRange checks both positive
and negative offsets.

ARMISelLowering has been tweaked because the test case presented
another pattern that we weren't supporting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365749 91177308-0d34-0410-b5e6-96231b3b80d8