skeleton: create include/ directory

skeleton: create include/ directory

Don't rely on a random host package to create the include/ directory for
us. Some packages do the wrong thing since they implicitly assume that
this directory exists already. Commit a557aedad2 (zstd: fix host headers
installation) shows an example of that.

Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>