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/Lex/Preprocessor.cpp b/lib/Lex/Preprocessor.cpp
index b6653fc..7033e9c 100644
--- a/lib/Lex/Preprocessor.cpp
+++ b/lib/Lex/Preprocessor.cpp
@@ -470,7 +470,7 @@
                                            Identifier.getLength()));
   } else {
     // Cleaning needed, alloca a buffer, clean into it, then use the buffer.
-    llvm::SmallString<64> IdentifierBuffer;
+    SmallString<64> IdentifierBuffer;
     StringRef CleanedStr = getSpelling(Identifier, IdentifierBuffer);
     II = getIdentifierInfo(CleanedStr);
   }