[lldb][Swift] Update swift performIRGen API

Update lldb's usage of swift compiler API after update.

(cherry picked from commit 117a1b7)

Author: cachemeifyoucan

lldb/source/Plugins/ExpressionParser/Swift/SwiftExpressionParser.cpp

@@ -2100,7 +2100,8 @@ SwiftExpressionParser::Parse(DiagnosticManager &diagnostic_manager,
         &parsed_expr->module, IRGenOpts, m_swift_ast_ctx.GetTBDGenOptions(),
         std::move(sil_module), "lldb_module",
         swift::PrimarySpecificPaths("", parsed_expr->main_filename),
-        llvm::ArrayRef<std::string>(), llvm::ArrayRef<std::string>());
+        /*CAS=*/nullptr, llvm::ArrayRef<std::string>(),
+        llvm::ArrayRef<std::string>());
     if (GenModule) {
       auto parse_result = verify(*GenModule.getModule());
       if (parse_result != ParseResult::success)