Add missing #include for linux.
Add missing #include for linux.

<rdar://problem/25501013>

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@272445 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit ae65fc8bc7d4af4b985fe64c51c8bcde7b21e5d4)

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb