Dirs created by GHC.Utils.TmpFs.newTempDir cannot be removed

GHC.Utils.TmpFs.newTempDir creates a new ghc_N subdirectory in a temp directory, but this directory cannot be removed. The result is a warning at the end of the GHC run.

It's not possible to clean this ghc_N subdirectory using addFilesToClean:

• addFilesToClean uses removeFile and fails for directories
• the to-clean list is kept in a Set FilePath and doesn't preserve the order in which the files were added, so a dir could potentially be removed before the files contained in it.

I've come up with two ideas to fix it

• when removing a top-level ghc temp dir, automatically remove empty ghc_N subdirs inside it (in cleanTempDirs)
• keep track of all created ghc_N by newTempDir and remove them as the first step in cleanTempDirs

Any preferences or other ideas?