[CodeView] Fix some Clang-tidy modernize-use-using and Include What You Use warnings; other minor fixes (NFC).

llvm-svn: 306616
diff --git a/llvm/lib/DebugInfo/CodeView/DebugCrossExSubsection.cpp b/llvm/lib/DebugInfo/CodeView/DebugCrossExSubsection.cpp
index 21e2cc5..cef2778 100644
--- a/llvm/lib/DebugInfo/CodeView/DebugCrossExSubsection.cpp
+++ b/llvm/lib/DebugInfo/CodeView/DebugCrossExSubsection.cpp
@@ -1,4 +1,4 @@
-//===- DebugCrossExSubsection.cpp -------------------------------*- C++ -*-===//
+//===- DebugCrossExSubsection.cpp -----------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -8,8 +8,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/DebugInfo/CodeView/DebugCrossExSubsection.h"
-
 #include "llvm/DebugInfo/CodeView/CodeViewError.h"
+#include "llvm/Support/BinaryStreamWriter.h"
+#include "llvm/Support/Error.h"
+#include <cstdint>
 
 using namespace llvm;
 using namespace llvm::codeview;