Tag build swift-DEVELOPMENT-SNAPSHOT-2017-03-09-a
Merge remote-tracking branch 'origin/swift-4.0-branch' into stable

* origin/swift-4.0-branch:
  [PGO] Suspend SIGKILL for PR_SET_PDEATHSIG in profile-write
  [PGO] Delay profile dir creation until write
  [compiler-rt][asan|win] Fix flaky unittest due to large allocations