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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294813 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/StringTableBuilder.cpp

@@ -1,4 +1,4 @@
-//===-- StringTableBuilder.cpp - String table building utility ------------===//
+//===- StringTableBuilder.cpp - String table building utility -------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -7,18 +7,24 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/MC/StringTableBuilder.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/MC/StringTableBuilder.h"
 #include "llvm/Support/COFF.h"
 #include "llvm/Support/Endian.h"
+#include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
-
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <utility>
 #include <vector>
 
 using namespace llvm;
 
-StringTableBuilder::~StringTableBuilder() {}
+StringTableBuilder::~StringTableBuilder() = default;
 
 void StringTableBuilder::initSize() {
   // Account for leading bytes in table so that offsets returned from add are