[clang] [clang][Dependency Scanning] Refactor Scanning Compiler Instance Initialization (PR #161300)

[Qiongsi Wu via cfe-commits]

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@@ -453,8 +583,18 @@ bool DependencyScanningAction::runInvocation(
             ScanInstance.getPreprocessorOpts().ImplicitPCHInclude, ScanInstance,
             ScanInstance.getHeaderSearchOpts().PrebuiltModuleFiles,
             PrebuiltModulesASTMap, ScanInstance.getDiagnostics(), StableDirs))
-      return false;
+      return {};
 
+  return PrebuiltModulesASTMap;
+}
+
+void clang::tooling::dependencies::initializeModuleDepCollector(
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qiongsiwu wrote:

Yeah this is a good idea! Thanks! The change I made has one difference from the above suggestion. I am keeping a copy of `DepOutOpts` in anticipation of reusing it when we share the compiler instance. 

https://github.com/llvm/llvm-project/pull/161300