Makefile: Add missing dependency (fix parallel builds)

The executables in i386-softmmu, i386-linux-user, ...
depend on the recently added libqemustub.a.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -127,6 +127,8 @@ pixman/Makefile: $(SRC_PATH)/pixman/configure
 $(SRC_PATH)/pixman/configure:
 	(cd $(SRC_PATH)/pixman; autoreconf -v --install)
 
+$(SUBDIR_RULES): libqemustub.a
+
 $(filter %-softmmu,$(SUBDIR_RULES)): $(universal-obj-y) $(trace-obj-y) $(common-obj-y) $(extra-obj-y) subdir-libdis
 
 $(filter %-user,$(SUBDIR_RULES)): $(universal-obj-y) $(trace-obj-y) subdir-libdis-user subdir-libuser