Basic: import IntrusiveRefCntPtr<> into clang namespace

The class name is long enough without the llvm:: added.
Also bring in RefCountedBase and RefCountedBaseVPTR.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150958 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/driver/driver.cpp b/tools/driver/driver.cpp
index e846b09..9e666eb 100644
--- a/tools/driver/driver.cpp
+++ b/tools/driver/driver.cpp
@@ -373,7 +373,7 @@
   TextDiagnosticPrinter *DiagClient
     = new TextDiagnosticPrinter(llvm::errs(), DiagnosticOptions());
   DiagClient->setPrefix(llvm::sys::path::stem(Path.str()));
-  llvm::IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
+  IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
   DiagnosticsEngine Diags(DiagID, DiagClient);
 
 #ifdef CLANG_IS_PRODUCTION