GHC should delete all temporary files it creates in /tmp
GHC creates large numbers of temporary files in /tmp. These would normally get cleaned up when the machine is rebooted, but for things like Jenkins build machines that don't get rebooted often they accumulate pretty quickly. The /tmp on my Jenkins build machine currently has over 200k files and directories, but only about 40 of them are non-GHC related files.
Under normal operation, GHC should delete all temporary files it creates.