scripts: target_config_lib: prepend target default package list from openwrt/tmp/.targetinfo

Device-specific package additions could generate `CONFIG_PACKAGE_...=m`
lines, which would override `CONFIG_PACKAGE_...=y` lines inserted by
OpenWrt for default packages (as Gluon did not know about these default
packages). This resulted in the unintended removal of such packages from
other devices that did not contain the same package in their device
package lists.

Avoid this issue by explicitly adding OpenWrt's target default package
list to the front of Gluon's target package list.

Makefile

@@ -181,6 +181,7 @@ config: $(LUA) FORCE
 		$(call CheckSite,$(conf)); \
 	)
 
+	$(OPENWRTMAKE) prepare-tmpinfo
 	$(GLUON_ENV) $(LUA) scripts/target_config.lua > openwrt/.config
 	$(OPENWRTMAKE) defconfig
 	$(GLUON_ENV) $(LUA) scripts/target_config_check.lua

scripts/target_config_lib.lua

@@ -154,12 +154,31 @@ local function handle_target_pkgs(pkgs)
 	end
 end
 
+local function get_default_pkgs()
+	local targetinfo_target = string.gsub(openwrt_config_target, '_', '/')
+	local target_matches = false
+	for line in io.lines('openwrt/tmp/.targetinfo') do
+		local target_match = string.match(line, '^Target: (.+)$')
+		if target_match then
+			target_matches = (target_match == targetinfo_target)
+		end
+
+		local default_packages_match = string.match(line, '^Default%-Packages: (.+)$')
+		if target_matches and default_packages_match then
+			return split(default_packages_match)
+		end
+	end
+
+	io.stderr:write('Error: unable to get default packages for OpenWrt target ', targetinfo_target, '\n')
+	os.exit(1)
+end
+
 lib.include('generic')
 lib.include(target)
 
 lib.check_devices()
 
-handle_target_pkgs(lib.target_packages)
+handle_target_pkgs(concat_list(get_default_pkgs(), lib.target_packages))
 
 for _, dev in ipairs(lib.devices) do
 	local device_pkgs = {}