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/TokenLexer.cpp b/lib/Lex/TokenLexer.cpp
index e036c42..5102cce 100644
--- a/lib/Lex/TokenLexer.cpp
+++ b/lib/Lex/TokenLexer.cpp
@@ -450,7 +450,7 @@
 /// are more ## after it, chomp them iteratively.  Return the result as Tok.
 /// If this returns true, the caller should immediately return the token.
 bool TokenLexer::PasteTokens(Token &Tok) {
-  llvm::SmallString<128> Buffer;
+  SmallString<128> Buffer;
   const char *ResultTokStrPtr = 0;
   SourceLocation StartLoc = Tok.getLocation();
   SourceLocation PasteOpLoc;