build system: don't let install-stubdom depend on install-tools

There is no reason for the install-stubdom target to depend on
install-tools. It is absolutely reasonable to install new stubdoms
only.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

Makefile

@@ -101,7 +101,7 @@ install-tools:
 	$(MAKE) -C tools install
 
 .PHONY: install-stubdom
-install-stubdom: install-tools mini-os-dir
+install-stubdom: mini-os-dir
 	$(MAKE) -C stubdom install
 ifeq (x86_64,$(XEN_TARGET_ARCH))
 	XEN_TARGET_ARCH=x86_32 $(MAKE) -C stubdom install-grub