skalibs: new package

skalibs: new package

This new package provides skalibs, a collection of free software / open
source C development files used for building all softwares from
skarnet.org.

Note that, though skalibs (and all skarnet softwares) follows the
"./configure; make; make install" convention, it does not behave like a
traditional autotools project:

 - static libraries are installed in $prefix/usr/lib/skalibs.
 - pkg-config and libtool are not used: instead a custom system called
   "sysdeps" is used and locations to libraries and headers are to be
   passed explicitly via options of the './configure' script.

The host variant is provided to allow building the host variants of the
other skarnet softwares.

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
[Thomas: remove post install target hook, do it directly in the target
installation commands.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>