Fix overflow testing in sbrk. am: 1944780b62 am: 3a5ebf3154  -s ours am: d95336ac42
am: 0993319651

* commit '099331965176b368af627858f087dc0eccd0fc18':
  Fix overflow testing in sbrk.

Change-Id: I4bb6ccba7238bb786eee22cb96b0bc64c3f534b8