fixup! pkg: ensure "dynamic sparse paths" are up-to-date

pkg/pkg.mk

@@ -134,12 +134,14 @@ $(PKG_DOWNLOADED): $(MAKEFILE_LIST) | $(PKG_SOURCE_DIR)/.git
 # E.g., build a) only needs CMSIS/Core. Build b) also needs CMSIS/DSP.
 # If b) is built after a) and the cmsis checkout does not contain CMSIS/DSP,
 # the sources need to be checked out again.
+# (Inside, this is doing an ad-hoc "|$(LAZYSPONGE)", but using the python version turned out
+# to be significantly slower).
 ifneq (, $(PKG_SPARSE_PATHS))
 PKG_SPARSE_TAG = $(PKG_SOURCE_DIR).sparse
 $(PKG_SPARSE_TAG): FORCE
 	$(Q)if test -f $@; then \
 		test "$$(cat $@)" = "$(PKG_SPARSE_PATHS)" && exit 0; \
-	fi ; echo HIT; echo "$(PKG_SPARSE_PATHS)" > $@
+	fi ; mkdir -p $((dirname $@)) && echo "$(PKG_SPARSE_PATHS)" > $@
 endif
 
 ifneq (,$(GIT_CACHE_RS))