[EXPERIMENTAL] Makefile: EXTRA_APPS_LIBS and EXTRA_APPS_INCPATHS vars

The variables are to be used to mainly by the export rule
to export external libraries (.a files) and respective include paths.

The exported external libraries are packed together in the libapps.a
library (basically, every .o files are extracted and then packed
together).

Signed-off-by: Stepan Pressl <pressl.stepan@gmail.com>

Makefile

@@ -197,6 +197,28 @@ preconfig: Kconfig
 export:
 ifneq ($(EXPORTDIR),)
 	$(Q) mkdir -p "${EXPORTDIR}"$(DELIM)registry || exit 1;
+	if [ -n "${EXTRA_APPS_LIBS}" ]; then \
+		mkdir -p $(APPDIR)$(DELIM)libcomb; \
+		cp libapps.a $(APPDIR)$(DELIM)libcomb; \
+		for l in ${EXTRA_APPS_LIBS}; do \
+			echo "AR: $$(basename $${l})"; \
+			cp $${l} $(APPDIR)$(DELIM)libcomb; \
+		done; \
+		cd $(APPDIR)$(DELIM)libcomb; \
+		for l in *.a; do \
+			$(AR_EXTRACT) $${l}; \
+		done; \
+		$(AR) libmerged.a *.o; \
+		mv libmerged.a ..$(DELIM)libapps.a; \
+		cd ..; \
+		rm -rf $(APPDIR)$(DELIM)libcomb; \
+	fi; \
+	for d in ${EXTRA_APPS_INCPATHS}; do \
+		if [ -d "$${d}" ]; then \
+			echo "CP: $$(basename $${d})" ; \
+			cp -r "$${d}" "${EXPORTDIR}"$(DELIM)include ; \
+		fi \
+	done
 ifneq ($(CONFIG_BUILD_KERNEL),y)
 ifneq ($(BUILTIN_REGISTRY),)
 	for f in "${BUILTIN_REGISTRY}"$(DELIM)*.bdat "${BUILTIN_REGISTRY}"$(DELIM)*.pdat ; do \