Fix build of DebugInfoPDBTests.

Missing a using statement.

llvm-svn: 268552
diff --git a/llvm/unittests/DebugInfo/PDB/PDBApiTest.cpp b/llvm/unittests/DebugInfo/PDB/PDBApiTest.cpp
index 736a6cc..cd0f928 100644
--- a/llvm/unittests/DebugInfo/PDB/PDBApiTest.cpp
+++ b/llvm/unittests/DebugInfo/PDB/PDBApiTest.cpp
@@ -50,6 +50,7 @@
 #include "llvm/DebugInfo/PDB/PDBTypes.h"
 #include "gtest/gtest.h"
 using namespace llvm;
+using namespace llvm::pdb;
 
 namespace {