[NFC] Add some missing header includes

[etcwilde]

Summary

Fixing local build failures due to missing header includes.

[etcwilde]

Grabbed the right patch

[mib]

LGTM!

clang/lib/Frontend/CachedDiagnostics.h

 //===- CachedDiagnostics.h - Serializing diagnostics for caching-*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_TOOLS_DRIVER_CACHEDDIAGNOSTICS_H
 #define LLVM_CLANG_TOOLS_DRIVER_CACHEDDIAGNOSTICS_H
 
 #include "clang/Basic/LLVM.h"
 #include "llvm/Support/PrefixMapper.h"
+#include <memory>
+#include <optional>
 
 namespace clang {
 class DiagnosticConsumer;
 class DiagnosticsEngine;
 class FileManager;
 
 namespace cas {
 

clang/lib/Frontend/CachedDiagnostics.cpp

 #include "CachedDiagnostics.h"
 #include "clang/Basic/DiagnosticCAS.h"
 #include "clang/Basic/SourceManager.h"
 #include "llvm/Support/Base64.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/EndianStream.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/YAMLTraits.h"
+#include <variant>
 
 using namespace clang;
 using namespace clang::cas;
 using namespace llvm;
 
 namespace {
 
 namespace cached_diagnostics {

llvm/include/llvm/Support/Format.h

 #define LLVM_SUPPORT_FORMAT_H
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DataTypes.h"
 #include <cassert>
 #include <cstdio>
+#include <optional>
 #include <tuple>
 #include <utility>
 
 namespace llvm {
 
 /// This is a helper class used for handling formatted output.  It is the
 /// abstract base class of a templated derived class.
 class format_object_base {

llvm/include/llvm/TargetParser/SubtargetFeature.h

 /// as example, gather chip info from the command line, a long with features
 /// that should be used on that chip.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_TARGETPARSER_SUBTARGETFEATURE_H
 #define LLVM_TARGETPARSER_SUBTARGETFEATURE_H
 
+#include "llvm/ADT/bit.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/MathExtras.h"
 #include <array>
 #include <initializer_list>
 #include <string>
 #include <vector>