check-package: support symlinks to the script

check-package: support symlinks to the script

The check-package script finds base_dir (= the Buildroot directory) and
cd's into it. To be able to support relative paths as arguments, it
first recalculates the arguments relative to base_dir.

However, if there is a symlink anywhere on the path to the
check-package script, the relative paths will be wrong. To solve this,
use realpath() instead of abspath(), so symlinks are resolved before
calculating the relative path.

Cc: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>