Perform the following transformation:

    | Before           | After               |
    |------------------+---------------------|
    | add w2, w0, w1   | adds w2, w0, w1     |
    | cmp w2, #0x0     | b.<cond'> <addr>    |
    | b.<cond> <addr>  |                     |
    |------------------+---------------------|
    | add w2, w0, w1   | adds w2, w0, w1     |
    | cmp #0x0, w2     | b.<cond'> <addr>    |
    | b.<cond> <addr>  |                     |

and the same for and instructions instead of add.  When the result of the
add/and is not used, generate cmn/tst instead. We need to take care with which
conditions we can handle and what new condition we map them to.

BUG=

Review-Url: https://codereview.chromium.org/2065243005
Cr-Commit-Position: refs/heads/master@{#37400}