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>
(cherry picked from commit 967d302e8bbb409c5b5106b0c87091d47f01a890)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/skeleton/skeleton.mk

@@ -16,6 +16,7 @@ SKELETON_ADD_SKELETON_DEPENDENCY = NO
 define HOST_SKELETON_INSTALL_CMDS
 	$(Q)ln -snf . $(HOST_DIR)/usr
 	$(Q)mkdir -p $(HOST_DIR)/lib
+	$(Q)mkdir -p $(HOST_DIR)/include
 	$(Q)case $(HOSTARCH) in \
 		(*64) ln -snf lib $(HOST_DIR)/lib64;; \
 		(*)   ln -snf lib $(HOST_DIR)/lib32;; \