Merge pull request #14677 from edx/nedbat/safer-make-clean

Safer "make clean"

Makefile

 # Do things in edx-platform
 
+# Careful with mktemp syntax: it has to work on Mac and Ubuntu, which have differences.
+PRIVATE_FILES := $(shell mktemp -u /tmp/private_files.XXXXXX)
+
 clean:
 	# Remove all the git-ignored stuff, but save and restore things marked
-	# by start-noclean/end-noclean.
+	# by start-noclean/end-noclean. Include Makefile in the tarball so that
+	# there's always at least one file even if there are no private files.
 	sed -n -e '/start-noclean/,/end-noclean/p' < .gitignore > /tmp/private-files
-	tar cf /tmp/private.tar `git ls-files --exclude-from=/tmp/private-files --ignored --others`
-	git clean -fdX
-	tar xf /tmp/private.tar
+	-tar cf $(PRIVATE_FILES) Makefile `git ls-files --exclude-from=/tmp/private-files --ignored --others`
+	-git clean -fdX
+	tar xf $(PRIVATE_FILES)
+	rm $(PRIVATE_FILES)