package/pkg-utils.mk: add extractor-pkg-dependency macro

package/pkg-utils.mk: add extractor-pkg-dependency macro

To extract some archive types, if the extracting tool is not available
on the system where Buildroot runs on, we build it using a Buildroot
host package.

Such dependencies are currently explicitly handled by the
inner-generic-package macro, but in fact we also need to handle them
in all places where the "suitable-extractor" macro is invoked, and
some packages invoke it directly. Otherwise, such packages may be
missing a dependency to the appropriate host Buildroot package
building the extracting tool they need. An example is gettext-tiny,
whose source code is a gzip-compressed tarball, but in addition
manually extracts a xz-compressed tarball.

This extractor-pkg-dependency macro will be used in follow-up commits
to ensure all the packages that use suitable-extractor properly add
the correct dependencies.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>