package/runc: add upstream security fix for CVE-2019-5736

The vulnerability allows a malicious container to (with minimal user
interaction) overwrite the host runc binary and thus gain root-level
code execution on the host. The level of user interaction is being able
to run any command (it doesn't matter if the command is not
attacker-controlled) as root within a container in either of these
contexts:

  * Creating a new container using an attacker-controlled image.
  * Attaching (docker exec) into an existing container which the
    attacker had previous write access to.

For more details, see the advisory:

https://www.openwall.com/lists/oss-security/2019/02/11/2



The fix for this issue uses fexecve(3), which isn't available on uClibc, so
add a dependency on !uclibc to runc and propagate to the reverse
dependencies (containerd/docker-engine).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>