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/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp b/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
index 93783fa..3e0ef21 100644
--- a/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
@@ -252,7 +252,7 @@
 }
 
 void ASTFieldVisitor::ReportError(QualType T) {
-  llvm::SmallString<1024> buf;
+  SmallString<1024> buf;
   llvm::raw_svector_ostream os(buf);
 
   os << "AST class '" << Root->getName() << "' has a field '"