Revert "Introduce a string_ostream string builder facilty"

Temporarily back out commits r211749, r211752 and r211754.

llvm-svn: 211814
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
index 680a7ec..4df5ede 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
@@ -268,7 +268,8 @@
 }
 
 std::string ScheduleDAGSDNodes::getGraphNodeLabel(const SUnit *SU) const {
-  string_ostream O;
+  std::string s;
+  raw_string_ostream O(s);
   O << "SU(" << SU->NodeNum << "): ";
   if (SU->getNode()) {
     SmallVector<SDNode *, 4> GluedNodes;