Fix rm command portability

Some implementations of rm(1) are stricter about the ordering of option
and non-option arguments as specified in POSIX.

Makefile.in

@@ -142,7 +142,7 @@ stamps/check-write-permission:
 		 "'$(INSTALL_DIR)', use --prefix to specify" \
 		 "another path, or use 'sudo make' if you *REALLY* want to" \
 		 "install into '$(INSTALL_DIR)'" && exit 1)
-	rm $(INSTALL_DIR)/.test -r
+	rm -r $(INSTALL_DIR)/.test
 	mkdir -p $(dir $@) && touch $@
 
 stamps/build-linux-headers: