[PATCH] [AArch64] Generate tbz/tbnz when comparing against zero.

[Xu Jiangwei]

The patch looks good, and I am researching an issue which is a bit like this one. I think there should be more test case, for example 
        cmp      w0, #1                 // =1
        b.lt    .LBB

http://reviews.llvm.org/D4440