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/ARCMigrate/TransUnbridgedCasts.cpp b/lib/ARCMigrate/TransUnbridgedCasts.cpp
index 3e5723d..48437c7 100644
--- a/lib/ARCMigrate/TransUnbridgedCasts.cpp
+++ b/lib/ARCMigrate/TransUnbridgedCasts.cpp
@@ -195,7 +195,7 @@
       TA.insertAfterToken(CCE->getLParenLoc(), bridge);
     } else {
       SourceLocation insertLoc = E->getSubExpr()->getLocStart();
-      llvm::SmallString<128> newCast;
+      SmallString<128> newCast;
       newCast += '(';
       newCast += bridge;
       newCast += E->getType().getAsString(Pass.Ctx.getPrintingPolicy());