Fix overflow testing in sbrk. am: 1944780b62 am: 3a5ebf3154  -s ours am: d95336ac42 am: 0993319651 am: 0ae30d9af8 am: 83b0671a33 am: 10a48fb557 am: fd84d78b1e am: b4d92e1362 am: ad80daaab5 am: 7189a4ccc2
am: d120719e25

* commit 'd120719e250d3f112b1c71ae775cab09c70191cd':
  Fix overflow testing in sbrk.

Change-Id: I4ab3da189f46d29b1e9fcd9737227e4fcf73221e