[Caching][NFC] Restructure CASOption in swift. NFC

Clean up how CASOptions are kept and passed inside swift to make the
code more readable. Also avoid a copy of CAS configuration in
ClangImporter.

lib/Basic/CASOptions.cpp

@@ -0,0 +1,39 @@
+//===--- CASOptions.cpp - CAS & caching options ---------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the CASOptions class, which provides various
+//  CAS and caching flags.
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/Basic/CASOptions.h"
+
+using namespace swift;
+
+void CASOptions::enumerateCASConfigurationFlags(
+      llvm::function_ref<void(llvm::StringRef)> Callback) const {
+  if (EnableCaching) {
+    Callback("-cache-compile-job");
+    if (!CASOpts.CASPath.empty()) {
+      Callback("-cas-path");
+      Callback(CASOpts.CASPath);
+    }
+    if (!CASOpts.PluginPath.empty()) {
+      Callback("-cas-plugin-path");
+      Callback(CASOpts.PluginPath);
+      for (auto Opt : CASOpts.PluginOptions) {
+        Callback("-cas-plugin-option");
+        Callback((llvm::Twine(Opt.first) + "=" + Opt.second).str());
+      }
+    }
+  }
+}