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.)

llvm-svn: 149799
diff --git a/clang/lib/Frontend/HeaderIncludeGen.cpp b/clang/lib/Frontend/HeaderIncludeGen.cpp
index f703674..79920df 100644
--- a/clang/lib/Frontend/HeaderIncludeGen.cpp
+++ b/clang/lib/Frontend/HeaderIncludeGen.cpp
@@ -108,10 +108,10 @@
   // are showing all headers.
   if (ShowHeader && Reason == PPCallbacks::EnterFile) {
     // Write to a temporary string to avoid unnecessary flushing on errs().
-    llvm::SmallString<512> Filename(UserLoc.getFilename());
+    SmallString<512> Filename(UserLoc.getFilename());
     Lexer::Stringify(Filename);
 
-    llvm::SmallString<256> Msg;
+    SmallString<256> Msg;
     if (ShowDepth) {
       // The main source file is at depth 1, so skip one dot.
       for (unsigned i = 1; i != CurrentIncludeDepth; ++i)