build: generate index.json

The index.json file lies next to Packages index files and contains a
json dict with the package architecture and a dict of package names and
versions.

This can be used for downstream project to know what packages in which
versions are available.

Signed-off-by: Paul Spooren <mail@aparcar.org>
(cherry picked from commit 218ce40cd7)

package/Makefile

@@ -92,6 +92,10 @@ $(curdir)/index: FORCE
 			$(call ERROR_MESSAGE,WARNING: Applying padding in $$d/Packages to workaround usign SHA-512 bug!); \
 			{ echo ""; echo ""; } >> Packages;; \
 		esac; \
+		echo -n '{"architecture": "$(ARCH_PACKAGES)", "packages":{' > index.json; \
+		sed -n -e 's/^Package: \(.*\)$$/"\1":/p' -e 's/^Version: \(.*\)$$/"\1",/p' Packages | tr '\n' ' ' >> index.json; \
+		echo '}}' >> index.json; \
+		sed -i 's/, }}/}}/' index.json; \
 		gzip -9nc Packages > Packages.gz; \
 	); done
 ifdef CONFIG_SIGNED_PACKAGES