(1) Added DSGraph::cloneReachableSubgraph and DSGraph::cloneReachableNodes

(1) Added DSGraph::cloneReachableSubgraph and DSGraph::cloneReachableNodes
    to clone the subgraph reachable from a set of root nodes, into the
    current graph, merging the global nodes into those in the current graph.
(2) Added DSGraph::updateFromGlobalGraph() to rematerialize nodes from the
    globals graph into the current graph in both BU and TD passes.
(3) Added hash_set<const GlobalValue*> InlinedGlobals: a set of globals to
    track which globals have been inlined into the current graph from
    callers or callees.  In the TD pass, such globals are up-to-date and
    do not need to be rematerialized from the GlobalsGraph.
(4) Added StripIncompleteBit/KeepIncompleteBit to remove incomplete bit
    when cloning nodes into the globals graph.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7190 91177308-0d34-0410-b5e6-96231b3b80d8