Add missing headers

[etcwilde]

Clang CachedDiagnostics uses std::unique_ptr, std::variant, and std::optional, coming from the memory, variant, and optional headers respectively. It looks like things shifted a bit so this wasn't building locally on Linux due to missing definitions.

llvm subtarget parser SubtargetFeature.h uses llvm::popcount, which comes from llvm/ADT/bit.h, which was causing build failures locally due to a missing llvm::popcount declaration.

Add missing optional include to include/llvm/Support/Format.h

[etcwilde]

@swift-ci please test

[etcwilde]

@swift-ci please test

[edymtt]

Thanks! That allowed me to clear errors related to SwiftRemoteMirror.cpp when building Swift for macOS against Xcode 14.2

[etcwilde]

swiftlang/swift#67170

@swift-ci please test

[etcwilde]

CMake version we're using is too old for LLVM:

CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.20.0 or higher is required.  You are running version 3.19.6

[etcwilde]

Alright, this gets us through the LLVM build and into Swift build failures due to leaky builds;

In file included from /Users/ec2-user/jenkins/workspace/apple-llvm-project-pr-macos/branch-next/swift/stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp:26:
In file included from /Users/ec2-user/jenkins/workspace/apple-llvm-project-pr-macos/branch-next/swift/include/swift/RemoteInspection/ReflectionContext.h:24:
In file included from /Users/ec2-user/jenkins/workspace/apple-llvm-project-pr-macos/branch-next/llvm-project/llvm/include/llvm/Object/COFF.h:26:
In file included from /Users/ec2-user/jenkins/workspace/apple-llvm-project-pr-macos/branch-next/llvm-project/llvm/include/llvm/TargetParser/SubtargetFeature.h:20:
/Users/ec2-user/jenkins/workspace/apple-llvm-project-pr-macos/branch-next/llvm-project/llvm/include/llvm/ADT/bit.h:115:51: error: redefinition of 'TrailingZerosCounter'
  115 | template <typename T, std::size_t SizeOfT> struct TrailingZerosCounter {
      |                                                   ^
/Users/ec2-user/jenkins/workspace/apple-llvm-project-pr-macos/branch-next/swift/stdlib/include/llvm/Support/MathExtras.h:91:51: note: previous definition is here
   91 | template <typename T, std::size_t SizeOfT> struct TrailingZerosCounter {
      |                                                   ^

(I think this is as good as we're going to get for a bit.)
I've opened https://reviews.llvm.org/D154664 on upstream LLVM so we'll get that landed there.

[etcwilde]

@swift-ci please smoke test