make: introduce pkg-prepare target

Makefile.include

@@ -328,7 +328,7 @@ include $(RIOTBASE)/drivers/Makefile.include
 
 # The `clean` needs to be serialized before everything else.
 ifneq (, $(filter clean, $(MAKECMDGOALS)))
-    all $(BASELIBS) $(USEPKG:%=$(RIOTPKG)/%/Makefile.include) $(RIOTBUILD_CONFIG_HEADER_C): clean
+    all $(BASELIBS) $(USEPKG:%=$(RIOTPKG)/%/Makefile.include) $(RIOTBUILD_CONFIG_HEADER_C) pkg-prepare: clean
 endif
 
 # include Makefile.includes for packages in $(USEPKG)
@@ -342,8 +342,11 @@ USEMODULE_INCLUDES_ = $(shell echo $(USEMODULE_INCLUDES) | tr ' ' '\n' | awk '!a
 
 INCLUDES += $(USEMODULE_INCLUDES_:%=-I%)
 
-.PHONY: $(USEPKG:%=${BINDIR}/%.a)
-$(USEPKG:%=${BINDIR}/%.a): $(RIOTBUILD_CONFIG_HEADER_C)
+.PHONY: pkg-prepare $(USEPKG:%=${BINDIR}/%.a)
+pkg-prepare:
+	-@for i in $(USEPKG) ; do "$(MAKE)" -C $(RIOTPKG)/$$i prepare ; done
+
+$(USEPKG:%=${BINDIR}/%.a): $(RIOTBUILD_CONFIG_HEADER_C) pkg-prepare
 	@mkdir -p ${BINDIR}
 	$(QQ)"$(MAKE)" -C $(RIOTPKG)/$(patsubst ${BINDIR}/%.a,%,$@)