packages: improve dependency check in virtual packages.

The current version of dependency check for virtual package <foo>
defines FOO_CONFIGURE_CMDS to print an error message if the
dependencies are not met.

This patch updates all the virtual packages to use the GNU Make control
function $(error text...) instead.

This makes the error happen at the beginning of the build, with a clearer
message.

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
package: normalize separator size to 80

Signed-off-by: Jerzy Grzegorek <jerzy.grzegorek@trzebnica.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
package/luainterpreter: rename the _HAS and _PROVIDES variables

The basic rule for a package is to have its options named
after the package name. There is no reason this should not
also be the case for virtual packages.

Besides, this will allow us to switch luainterpreter to use the
soon-to-be-introduced virtual-package infrastructure.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Mike Zick <minimod@morethan.org>
Cc: Francois Perrad <fperrad@gmail.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
package/lua: rename config options

Package's options should be named after the package.

Lua is an interpreter, but the package is named 'lua'. So we want to
name the config option with '_LUA_', not with '_LUA_INTERPRETER_'

Besides, naming them with '_LUA_INTERPRETER_' might be confusing, since
there is a package named 'luainterpreter'.

Since the renamed options are part of a choice, we can't use the legacy
options to select the new ones. So we instead instruct the user to go
select the appropriate option in the choice.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Francois Perrad <fperrad@gmail.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
packages: add infrastructure for virtual packages

The virtual-package infrastructure allows to easily define a
virtual package in a single line:

    $ cat package/some-virtual-package/some-virtual-package.mk
    $(eval $(virtual-package))

And that's all. :-)

Thanks to Éric for his work on the manual, that prompted the
idea for this virtual-package infrastructure! ;-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Mike Zick <minimod@morethan.org>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
package/luainterpreter: convert to the virtual-package infrastructure

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Mike Zick <minimod@morethan.org>
Cc: Francois Perrad <fperrad@gmail.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
virtual-package: fake a version string for virtual packages

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>