For info for anyone reading this now, there's now a platform of the R-hub package builder that has long doubles disabled.
You can use its online version,
rhub::check(<pkg-path>, platform = "debian-gcc-devel-nold")
Or run a local check if your OS is not Windows,
rhub::local_check_linux(<pkg-path>, image = "rhub/debian-gcc-devel-nold")
More info about rhub