Let the CompilerInstance create our clang ASTContext

[teemperor]

Summary

Now that we moved the BuiltinContext and SelectorTable to the
CompilerInstance, we can also get rid of manually creating our
own ASTContext, but just use the one from the CompilerInstance
(which will be created with the same settings).

[teemperor]

• clang-format.

source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp

ClangExpressionParser::ClangExpressionParser(ExecutionContextScope *exe_scope,
   // additionally enabling them as expandable builtins is breaking Clang.
   m_compiler->getLangOpts().NoBuiltin = true;
 
   auto &PP = m_compiler->getPreprocessor();
   auto &builtin_context = PP.getBuiltinInfo();
   builtin_context.initializeBuiltins(PP.getIdentifierTable(),
                                      m_compiler->getLangOpts());
 
-  std::unique_ptr<clang::ASTContext> ast_context(
-      new ASTContext(m_compiler->getLangOpts(), m_compiler->getSourceManager(),
-                     m_compiler->getPreprocessor().getIdentifierTable(),
-                     PP.getSelectorTable(), builtin_context));
 
-  ast_context->InitBuiltinTypes(m_compiler->getTarget());
+  m_compiler->createASTContext();
+  clang::ASTContext& ast_context = m_compiler->getASTContext();
 
   ClangExpressionHelper *type_system_helper =
       dyn_cast<ClangExpressionHelper>(m_expr.GetTypeSystemHelper());
   ClangExpressionDeclMap *decl_map = type_system_helper->DeclMap();
 
   if (decl_map) {
     llvm::IntrusiveRefCntPtr<clang::ExternalASTSource> ast_source(
         decl_map->CreateProxy());
-    decl_map->InstallASTContext(*ast_context, m_compiler->getFileManager());
-    ast_context->setExternalSource(ast_source);
+    decl_map->InstallASTContext(ast_context, m_compiler->getFileManager());
+    ast_context.setExternalSource(ast_source);
   }
 
   m_ast_context.reset(
       new ClangASTContext(m_compiler->getTargetOpts().Triple.c_str()));
-  m_ast_context->setASTContext(ast_context.get());
-  m_compiler->setASTContext(ast_context.release());
+  m_ast_context->setASTContext(&ast_context);
 
   std::string module_name("$__lldb_module");
 
   m_llvm_context.reset(new LLVMContext());
   m_code_generator.reset(CreateLLVMCodeGen(
       m_compiler->getDiagnostics(), module_name,
       m_compiler->getHeaderSearchOpts(), m_compiler->getPreprocessorOpts(),
       m_compiler->getCodeGenOpts(), *m_llvm_context));