fix build issues with SMP compiles

git-svn-id: svn://svn.openwrt.org/openwrt/branches/buildroot-ng/openwrt@4317 3c298f89-4303-0410-b956-a3cf2f4a3e73

include/package.mk

@@ -220,7 +220,7 @@ define BuildPackage
 
   clean: $(1)-clean
 
-  $(PKG_BUILD_DIR)/.version-$(1)_$(VERSION)_$(PKGARCH):
+  $(PKG_BUILD_DIR)/.version-$(1)_$(VERSION)_$(PKGARCH): $(PKG_BUILD_DIR)/.prepared
 	-rm $(PKG_BUILD_DIR)/.version-$(1)_*
 	@touch $$@