[include-cleaner] Ignore the layering-violation errors for the standalone tool

[hokein]

Summary

If the source code is compilable-but-layzering-violation, we still want
the tool to be functional on it (rather than bailing out).

[kadircet]

clang-tools-extra/include-cleaner/tool/IncludeCleaner.cpp

99

maybe mention the general stance against diagnostics here?

We only want to perform include-cleaner analysis. So we disable diagnostics that won't affect our analysis to make the tool more robust against in-development code.

and then follow up with specific around disabling decluse

clang-tools-extra/include-cleaner/test/Inputs/modules/a.h

+#pragma once
+class A {};

clang-tools-extra/include-cleaner/test/Inputs/modules/module.map

+module XA {
+}

clang-tools-extra/include-cleaner/test/module.cpp

+// RUN: cp %s %t.cpp
+// RUN: clang-include-cleaner -edit %t.cpp -- -I%S/Inputs/modules -fimplicit-module-maps -fmodules-strict-decluse -fmodule-name=XA
+// RUN: FileCheck --match-full-lines --check-prefix=EDIT %s < %t.cpp
+
+// Verify the tool still works on compilable-but-layering-violation code.
+#include "a.h"
+// EDIT-NOT: {{^}}#include "a.h"{{$}}

clang-tools-extra/include-cleaner/tool/IncludeCleaner.cpp

format::FormatStyle getStyle(llvm::StringRef Filename) {
   return std::move(*S);
 }
 
 class Action : public clang::ASTFrontendAction {
   RecordedAST AST;
   RecordedPP PP;
   PragmaIncludes PI;
 
+  bool BeginInvocation(CompilerInstance &CI) override {
+    // We only perform include-cleaner analysis. So we disable diagnostics that
+    // won't affect our analysis to make the tool more robust against
+    // in-development code.
+    CI.getLangOpts().ModulesDeclUse = false;
+    CI.getLangOpts().ModulesStrictDeclUse = false;
+    return true;
+  }
+
   void ExecuteAction() override {
     auto &P = getCompilerInstance().getPreprocessor();
     P.addPPCallbacks(PP.record(P));
     PI.record(getCompilerInstance());
     ASTFrontendAction::ExecuteAction();
   }
 
   std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,