Revert "Introduce a string_ostream string builder facilty"

Temporarily back out commits r211749, r211752 and r211754.

llvm-svn: 211814
diff --git a/llvm/lib/DebugInfo/DWARFDebugFrame.cpp b/llvm/lib/DebugInfo/DWARFDebugFrame.cpp
index 2227260..a33548e 100644
--- a/llvm/lib/DebugInfo/DWARFDebugFrame.cpp
+++ b/llvm/lib/DebugInfo/DWARFDebugFrame.cpp
@@ -353,9 +353,10 @@
     Entries.back()->parseInstructions(Data, &Offset, EndStructureOffset);
 
     if (Offset != EndStructureOffset) {
-      string_ostream Str;
-      Str << format("Parsing entry instructions at %lx failed", StartOffset);
-      report_fatal_error(Str.str());
+      std::string Str;
+      raw_string_ostream OS(Str);
+      OS << format("Parsing entry instructions at %lx failed", StartOffset);
+      report_fatal_error(Str);
     }
   }
 }