samples/check-exec: Add set-exec

samples/check-exec: Add set-exec

Add a simple tool to set SECBIT_EXEC_RESTRICT_FILE or
SECBIT_EXEC_DENY_INTERACTIVE before executing a command.  This is useful
to easily test against enlighten script interpreters.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241212174223.389435-6-mic@digikod.net
Signed-off-by: Kees Cook <kees@kernel.org>