Basic: import SmallString<> into clang namespace

(I was going to fix the TODO about DenseMap too, but
that would break self-host right now. See PR11922.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149799 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/LogDiagnosticPrinter.cpp b/lib/Frontend/LogDiagnosticPrinter.cpp
index 8eb4673..3fee957 100644
--- a/lib/Frontend/LogDiagnosticPrinter.cpp
+++ b/lib/Frontend/LogDiagnosticPrinter.cpp
@@ -64,7 +64,7 @@
     return;
 
   // Write to a temporary string to ensure atomic write of diagnostic object.
-  llvm::SmallString<512> Msg;
+  SmallString<512> Msg;
   llvm::raw_svector_ostream OS(Msg);
 
   OS << "<dict>\n";
@@ -140,7 +140,7 @@
   DE.DiagnosticLevel = Level;
 
   // Format the message.
-  llvm::SmallString<100> MessageStr;
+  SmallString<100> MessageStr;
   Info.FormatDiagnostic(MessageStr);
   DE.Message = MessageStr.str();