Iterates over all configured modules and checks them for updates.

Forgetting to `make update` or leaving uncommitted changes in the
repositories managed by Gluon is a recurring cause of confusion, even
for experienced developers. Let's print an obvious warning message in
this case.

GLUON_AUTOUPDATER_BRANCH and GLUON_AUTOUPDATER_ENABLED should be set
separately now.

This change stores a Kernel with Debug-Symbols for the current
architecture in a new output directory '<outputdir>/debug'.
This allows a developer or operator of a network to store the kernel
along with the actual images. In case of a kernel oops the debug
information can be used with the script
'scripts/decode_stacktrace.sh' in the kernel source tree to get the
names to the symbols of the stack trace.

OpenWRT already provides the CONFIG_COLLECT_KERNEL_DEBUG -option that
creates a kernel with debug-symbols in the OpenWRT output directory.
This change enables this option and copies the generated kernel to the
gluon output directory.

Signed-off-by: Chrissi^ <chris@tinyhost.de>

This reverts commit 2a8943e5.

.SILENT gets passed down to OpenWrt make as -s through MAKEFLAGS. This
hides certain messages from the build log with V=s.

The precedence of different package lists was broken since #1876,
disallowing removal of GLUON_FEATURES packages via GLUON_SITE_PACKAGES.

Including all package selections, both implicit defaults and explicit
handling in Gluon, the order of precedence is now the following:

1.  OpenWrt defaults (including target-specific defaults)
2.  Device-specific packages from OpenWrt
3.  Generic default packages (from target/generic)
4.  Target default packages (target/$(GLUON_TARGET))
5.  Removal of opkg for tiny targets
6.  Packages derived from GLUON_FEATURES + GLUON_FEATURES_$(class)
7.  GLUON_SITE_PACKAGES
8.  GLUON_SITE_PACKAGES_$(class)
9.  Device-specific packages from target/$(GLUON_TARGET)
10. Device-specific packages from GLUON_$(device)_SITE_PACKAGES

This also contains various pieces of cleanup:

- No hardcoded order of device classes for target_config.lua arguments
  anymore (in fact, the Makefile doesn't know anything about device
  classes now)
- target_conifg_lib.lua only hardcodes the fallback class for x86, no
  other occurences of specific class names
- Feature -> package list mapping is moved from Makefile to the Lua code
  as well (still implemented in Shell though)

Instead of exporting various variables (unintendedly making them
available to the OpenWrt build, possibly bypassing .config), pass the
environment only to commands that need it.

By using .ONESHELL and adding -e to .SHELLFLAGS, we can simplify complex
shell commands (like manifest generation) and gain a simple way to pass
multi-line environment variables into shell commands.

The @ and + flags for recipe commands are moved to the top of each
recipe.

This allows to define a list of packages, which are only installed
for a specific device-class.

This commit allows to define a device-class flag in the target
definitions. This way, it is possible to distinguish between groups
of devices in the build-process in terms of package or feature
selection.

[Matthias Schiffer: minor script improvements]

This new build flag is mandatory for now (it may default to 0 in a future
Gluon version). It may be set to the following values:

* 0 - Do not build any images for deprecated devices.
* upgrade - Only build sysupgrade images for deprecated devices.
* full - Build both sysupgrade and factory images for deprecated devices.

"Other" images are handled like factory images, as they are also used for
the initial installation of Gluon on a device.

The old bash-based parsing code was way too complex. Replace it with Lua.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

By passing the package name through merge_packages, it becomes possible to
override the package choice in GLUON_SITE_PACKAGES again, for example:

	GLUON_SITE_PACKAGES += -hostapd-mini hostapd

The domain configs are not checked yet, and not used for anything.

Based-on-patch-by: lemoer <git@irrelefant.net>

defaults to 11s, allowing to build devices without IBSS-support

obsoletes GLUON_ATH10K_MESH

Allow using relative paths for GLUON_SITEDIR, GLUON_OUTPUTDIR, ...

We also check for whitespace in paths now, as build will not work properly
with whitespace anyways, and Make's abspath would require escaping
otherwise.

[Matthias Schiffer: minor changes, rewrite commit message]

As the default package list is now handled using the 'packages' directive,
explicit wpad-mini removals in target definitions can be dropped.

This, together with a new try_config directive, will allow checking the
generic config and make it more flexible.

.SHELLSTATUS was not available before Make 4.2.

To reduce the number of packages that need to be listed in
GLUON_SITE_PACKAGES, this adds a new variable GLUON_FEATURES. Sets of
packages are enabled automatically based on the combination of listed
feature flags.

Site-specified package feeds can provide their own feature flag
definitions.

`make show-release` can be used to discover the current release in scripts.