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/HeaderMap.cpp b/lib/Lex/HeaderMap.cpp
index 9a0b4e9..bbfc1df 100644
--- a/lib/Lex/HeaderMap.cpp
+++ b/lib/Lex/HeaderMap.cpp
@@ -220,7 +220,7 @@
 
     // If so, we have a match in the hash table.  Construct the destination
     // path.
-    llvm::SmallString<1024> DestPath;
+    SmallString<1024> DestPath;
     DestPath += getString(B.Prefix);
     DestPath += getString(B.Suffix);
     return FM.getFile(DestPath.str());