Add a Build/InstallDev so libapparmor's header (sys/apparmor.h), the
libapparmor.so link and the pkg-config file are copied into the staging
directory. Without this, packages cannot build against libapparmor even
though the runtime shared library is provided; e.g. stress-ng's AppArmor
stressors fall back to "built without sys/apparmor.h".
Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>