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/TargetSchedule.cpp b/llvm/lib/CodeGen/TargetSchedule.cpp
index d18a514..b0f2ca6 100644
--- a/llvm/lib/CodeGen/TargetSchedule.cpp
+++ b/llvm/lib/CodeGen/TargetSchedule.cpp
@@ -212,10 +212,11 @@
   if (SCDesc->isValid() && !DefMI->getOperand(DefOperIdx).isImplicit()
       && !DefMI->getDesc().OpInfo[DefOperIdx].isOptionalDef()
       && SchedModel.isComplete()) {
-    string_ostream Err;
-    Err << "DefIdx " << DefIdx << " exceeds machine model writes for "
-        << *DefMI;
-    report_fatal_error(Err.str());
+    std::string Err;
+    raw_string_ostream ss(Err);
+    ss << "DefIdx " << DefIdx << " exceeds machine model writes for "
+       << *DefMI;
+    report_fatal_error(ss.str());
   }
 #endif
   // FIXME: Automatically giving all implicit defs defaultDefLatency is