Fix overflow testing in sbrk. am: 1944780b62 am: 3a5ebf3154  -s ours am: d95336ac42 am: 0993319651
am: 0ae30d9af8

* commit '0ae30d9af8c55d95edf7ddb1c2cb4f9dc0579f83':
  Fix overflow testing in sbrk.

Change-Id: I2d63124f58990f8ae3db35789bdd993d98d389ab