Missing import causing error on compilation (#2934)

Replaced <iostream> to <ios> in files using std::hex

lib/DxilRootSignature/DxilRootSignatureValidator.cpp

@@ -26,7 +26,7 @@
 #include <utility>
 #include <vector>
 #include <set>
-#include <iostream>
+#include <ios>
 
 #include "DxilRootSignatureHelper.h"
 

tools/clang/unittests/dxc_batch/dxc_batch.cpp

@@ -37,7 +37,7 @@
 #include <comdef.h>
 #include <thread>
 #include <unordered_map>
-#include <iostream>
+#include <ios>
 
 #include "llvm/Support//MSFileSystem.h"
 #include "llvm/Support/CommandLine.h"